Often its not just hardware but the drivers aren't updated and won't work on modern OS's. Mac users have just gone through the switch to Intel chips where old PowerPC programs wont work on the last two OSs and Windows has been threatening for years to rewrite an upcoming Windows that'll be completely incompatible with new hardware.
True, but given that a good modern computer exceeds the computing power needed by pretty much anybody apart from serious film composers; it wouldn't be the end of the world just to say 'this operating system and computer is good enough for me for the next eight to ten years'.
This is especially true if you bounce your software synths and Kontakt instruments down to audio.
Sound Artist and Composer