On it's own, the keyboard is lifeless, it gets it's power from the computer, sounds et al.
There ARE keyboards with extensive sound libraries built in AND midi capabilities, that you can plug in to a computer and use as a controller, or play it without a computer, but they cost $$$ to get one that is any good that is
the beauty part about software triggering is that it's infinitely more expandable and update-able, sampling software will improve, sounds will get more and more life like, and your keyboard will still work just fine.
remember, MIDI is a VERY old technology, dating back about 30 years, keyboards and triggers from back then STILL work just as fine today as they did in then.
The $99, 49 key M-audio keyboard apple is selling is a GREAT keyboard, I find that about 80% of the time when I am making music with midi(reason) the 49 key, keyboard I use is just fine. Some people like to have weighted keys, some people like o have 61 or even full sized 88 key keyboards. and that's fine, but for what I do, I rarely need to be playing out of the 4 octave range the 49 key provides.
That said, 2 octave keyboards like the Ozone8 or the oxygen8, I CANNOT work with, I am always limited with those, because the music I creat requires more than just one button at a time, I do chords and stuff, so that just doesn't work well for me.
but for general use 49 keys is just fine.
Remeber, you're a powerbook user, you don't want to bog down your portable music product capabilities with a 61 key keyboard.
which is another thing entirely, USB keyboards are great because they are far more portable than midi keyboards using USB midi hubs, so that's a big advantage.
I too am VERY excited about garageband, I'm going to the berklee school of music in a week, it will be a great compliment to reason, finale, and whatever else I'll be using.
if anything, garageband will definitely help to keep music making FUN, which is what it should be, programs that are a chore to use, undermine a big part about what makes music so great, imo