>>5
nothing extra is needed for backward compatibility
DOSBox, VDMSound and other virtualization tools people need to use to get pre Win95 software to work would like a word. Modern PC games generally require so little configuration they practically might as well be running on consoles, but running DOS-based titles on a modern PC is likely harder now than it was back then - you still have to do all the abstruse config.sys/autoexec.bat environment tampering, on top of basically hiding the Windows environment from the game, and you may even need to resort to digging around for third-party VESA hacks, game exe patches, mouse drivers and so on. If you play more than one or two DOS games with any regularity, though, you're probably better off just devoting a piddly little partition to a real DOS installation and multi-booting it, always assuming you can find drivers to make DOS recognize your hardware without things like the basic Soundblaster emulation XP does by default.
Console back-compat is a breeze: it should usually work, and if it doesn't you're fucked unless the hardware producer can be bothered to fix it. Xenogears is the only case I'm familiar with of a game that'd lock up a PS2 running default backward-compatibility settings, but I like to think that was the console developing rudimentary sentience to protest against such irredeemable crap.