In the area of a high quality bass amplifier, I’m afraid that the industry has really let us down. First of all you need to understand that if you want a high quality tone from your low end, then the speaker’s frequency response is crucial. The E sting on the bass vibrates at approximately 41.2 Hz. So, you need to have a frequency response out of your speakers that is actually lower than that. That is called head room (or bottom room as the case may be). So, a frequency response of 38 Hz or below is probably adequate for a 4-string bass. The 5-string has a lower B string that vibrates at approximately 30.87 Hz. So in that case, you’ll need head room down to around 28 Hz to provide a high quality bass sound. DO NOT BE CONFUSED BY Frequency Range vs Frequency Response. A speaker can have the range of 28 Hz or 38 HZ but, the Frequency Response is what is important for adequate quality of sound. So, in my case (5-sting) there are NO bass speaker cabinets on the market that will take you to a 28 Hz response without spending huge amounts of money and many of those speaker cabinets weigh as much as 200 pounds (no, I’m not kidding). That’s a real problem to haul it around. So, after looking at all of the available options, I decided that the best and least expensive route was to first get a BOSS GT-10B Bass Multi-effects pedal which acts as a pre-amplifier and provides any possible sound I could want out of my bass, and then I run that through a QSC GX5 500 watts/channel stereo amplifier and that amp drives twin JBL JRX115 2-way Speaker cabinets http://www.guitarcenter.com/JBL-JRX115-15–2-Way-Speaker-Cabinets—Pair-773198-i1152805.gc (I need the 2-way because I sing and play guitar also so I need the high tones as well as the lows). But, the Frequency response on these speakers is only down to 50 Hz. That’s adequate for the A string on the bass but not the E or the B on my 5-string. So, I added twin JBL ES250PBK 400-Watt High-Powered 12-Inch Subwoofers that provide a frequency response down to 28 Hz (weigh less than 60 pounds each and cost only around $300 each) and now when I play a gig, I have other bass players coming up to me all the time asking what kind of amplifier I have that is turning out the awesome bass sounds. When I play, it’s that kind of bass sound that you feel even before you are aware of hearing it. So, when I practice at home, I just use the Boss GT-10B and a great set of head phones so, I don’t distrub the rest of the neighborhood. If you want that kind of sound, that’s what you need to do. The alternative for a 4-sting weighing in at 166-1/2 pounds is this little baby – http://pro-audio.musiciansfriend.com/product/JBL-SRX728S-Dual-18-Subwoofer?sku=600444 – but, the catch is it will only handle bass notes up to around 220 Hz or the third octave A right below middle C. The bass has notes that go much higher than that. So, that means, you still need to buy another speaker cabinet (12"ers maybe & spend another $800 to $1,200 perhaps) to handle those notes (220 Hz up to around 530 Hz). So, go figure!

But a better brand would be VOX.
Most vox’s already have settings on and they are pretty good, they also let you make your own sounds too (like normal amps).

Id go for a vox

http://www.zzounds.com/cat–Acoustic-Guitar-Amps–2589

The speakers in guitar cabinets are specially designed for guitars. Celestion is the big name in guitar speakers. Head over to their site and you can see response curves and all sorts of great stuff about their speakers:

http://professional.celestion.com/guitar/

But to answer your question: they are simply designed that way. They are special speakers designed to reproduce the frequencies that guitars and amps can generate, a part of that is high frequencies.

First, the fender frontman is a very nice little amp and as a fender it is definitely going to give you some nice clean tones (as one other person pointed out) that are very useful in certain styles of music such as jazz and blues (think about some of Stevie Ray Vaughn’s music and you’ll know what I’m talking about, though he also made very good use of some dirty tones as well).

Which leads me to my next point, style of music is also going to be a factor in how you set up your amp. If you are going for that classic rock sound, then one nice thing you can do with fender amps is to lower the bass a bit and crank the mid and the treble and get some really nice crunchy tones.

One more thing to think about is the type of guitar you are using (and even the pick you are using to play it with) can affect how you’ll want to adjust the settings on your amp.

These are all basically ideas on what will play a role on how you’ll want to set your controls. My biggest suggestion for you, however, is not to settle for what sounds OK, play with the controls until you get the tone that you LOVE out of this amp. What I generally do is to take a new amp and put all the controls in the 12 o’clock position and adjust from there and play with it until I get something that I personally feel is a great sound. There’s a good chance that you’ll find what someone else tells you is a good sound is not necessarily the sound you’ll fall in love with from your amplifier. This is one way to define what YOU sound like.

My advice however is to wait until you can afford a real amplifier. While you can find good deals, you’re really not likely to find anything truly decent for under 500 bucks.

Most guitar players will argue that an all tube amp sounds better, more "musical", richer in nuances and responds better. However, they are also more expensive, much heavier, gets hot, are more fragile and more costly to repair and keep running smoothly over the years.

Transtube is a phrase coined by Peavey amplification. Here one uses the other common way of of amplification, transistors, in the power amp stage and preamp tube/valve to simulate some of the characteristics of a tube amp.

There are many great sounding and affordable amps that uses this combination of a transistor power amp and a tube preamp.

Model amps is a term used of hybrid amps who models (claim to sound like) other well known tube amp types, like Marshall, Fender, Vox and Mesa Boogie. There is usually many models built into one of these amps. They are digital in nature, but some also has the preamp tube variety added.

Not sure if this made it any clearer for you?