[psimancer]

as a computer shop owner for 5 years (1995-2000) and still mildly follow the market

you are correct theyt do make changes every 5 years or so to force a repurchase

example basic motherboard slots

isa vs mca (the pc xt era)
isa was 16 bit mca was vastly better at 32and nearly as fast at data transfer as a pci howwever the isa added two options to compete eisa (extended ) which worked very well and was backward compatible
and vesa an extended slot design that cost more and only 3 slots per machine instead of all eight (thats right EIGHT SLOTS !!!!!) vesa was replaced by pci losing its backward compatible slot design the first instance of a completly non backward compatible design replacing and winning in popularity (note the user base attitude change from tech heads who understood what they were buying and the implications of compatibility and later addons or replacement of a board vs today's userbase that says fix my computer toaster please )then next step was shrinking the motherboard and the case thus forcing fewer slots (cost reduction) now standard at 1 to 3 plus an agp if not a builtin card then as a addon agp the accerlerated graphics port came in to promise faster graphics vs pci slots and now pci express is attempting to replace the agp with an extension of the pci slot standard

the computer industry has to change standards to force business users to change machinery every few years otherwise business the mainstay of the industry would still be running there programs on 80386 computers which can handle most business applications (properly programmed with good tight code) and only purchase faster machines for programs that required the massive bloated power needed for windows and its overblown interface (yes i run wxp pro i havent really become happy with linux like tomany old programs i have)