Your initial point about the hardware not being available anymore is completely false. Every generation of Sony hardware PS 1, 2, and 3 can play every ps1 game. The removal of ps2 compatibility in the ps3 did not take away the ability to play ps1 games.
But what about attaching PS2 controllers to a PC? I appreciate that an adapter would be required, but do these differ? Which adapters are supported by which emulators? Will the adapters also support the early (non-USB) Guitar Hero controllers? Would be great to get rid of the PS2 under my media center PC, replacing it with an emulator.