Win98 is far more susceptible to viruses than 200 or XP, its security is almost non-existent, and there aren't a great deal of viruses that won't infect a 98 machine but will infect a 2000 machine.
The pain and hassles of running 98 vs running XP is quite frankly insane.
At the very least people can dual boot and have an NTFS partition.
Releasing as non image files is a pain, and would inconvenience the bulk of the people out there who run an OS that doesn't have an archaic file system, and only benefit the very few 98/95 users that still exist that run DVD burners...

Seriously, upgrade (or switch to linux if you are strapped for cash, or at least dual boot) and bring yourself into the current century, the water is just fine.