Firefox works on Windows 98,Me,2000,XP,Linux,Macintosh etc...
How many Windows NT or 98 boxes could run XP properly? 98 came out in 1998 and xp in 2001 - only 3 years difference. Now we are talking about 5+ years difference and a lot of hardware changes, 64 bit processors, SATA, SAS, Flat panels the list is endless.

There is nothing unfair or unusual going on here. You might 'want' to 'upgrade' to Vista but you do not have to. Lots of people still happily use Windows 98, 2000, MacOS8.5,9 Suse9 etc...

Feed the Beast or not the choice actually IS yours.