Because the way to go is to use memory cards (unfortunately, there are four in use -- Compact Flash (most popular), Smart Media, Memory Stick (Sony only), and MMC/SD (mainly Matsushita)).
I haven't tried a USB flash card reader on Linux yet, but I'd guess there are drivers. I'm pretty sure there are also Linux USB drivers for a variety of cameras, but I prefer the flash card approach (no stupid little proprietary cables to worry about).
For CF, the cheapest way to go is to get a CF-to-PCMCIA adapter ($12 or so) -- that should work fine!
Also, I highly recommend you at least look at LCD monitors. I love my 17" Planar LCD.
Tony