You CAN use Windows 7 apps on Win8 and Pro. RT is another story.

Yes, you can't use XP applications on Windows 8. Continued use of Office XP or '07 when you're upgrading to Windows 8 is the real question. Is it being cheap? I can't use newer apps on an iPhone 3GS because it can't be upgraded to iOS 5 or 6, but I understand that. At some point in the pursuit of continuing said business you have to force customers off your discontinued products. It's not just to sell the new stuff but to inform customers the old stuff cannot be supported or repaired. Donate your old stuff to poor folks in other countries. Deduct it on your tax forms. Move on already.