I think I read from one of the other threads about this...
The pay is usually very little at the start, and it helps to get a LOT of experience and work done for free, just so you can have a big showcase for your portfolio when you come to apply for working for real money..
Also, I'd imagine that with just Photoshop, the extent of work you'd be able to get is for photographers, artists, and if you're lucky, a small design studio, whereas if you have the whole suite of photoshop, indesign, illustrator, flash, etc, you might be at an advantage when you apply for work at bigger design studios, graphic designers, etc. AND, at this day and age, I would guess that web design would be more desirable...
Anyway, just my thoughts.. I've only got experience in photoshop and indesign, and that's why I'm here ^^