The entire modern UI was built to showcase the apps in Microsoft's new Windows Store--but Windows 8 also runs the classic desktop software you know and love. Heck, you can still pop open the command line in Microsoft's latest and greatest, so you still have the ability to run all those ancient DOS programs you probably should've forgotten about years ago.
Microsoft doesn't leave programs behind, no matter how outdated they are. (Yet.) Compare that with Apple's approach of ruthlessly killing off software the second it even starts to smell stale.