A total Linux newbie would get as far as downloading the demo.. finding it doesnt work and moving on.
However, since such a person does not exist, it's not exactly going to be a problem. Yes it would be easier if you could just apt-get install BlitzMAX, and everything would work. However since BlitzMAX needs to also run on inferior OSes that don't use libapt, there really doesn't seem to be any alternative. Up until now I've had an ATI card and they've been a real pain in the ass!
Well that's going to improve soon as AMD are open sourcing their drivers. Unfortunately some parts of the ATi drivers still use non-free source code, but once replacement source code has been written, I think you'll find AMD/ATi to be the champions of Linux graphics cards (and it's probably going to do wonders for the other platforms as well).