For the set of old apps Windows 8 is the same as Windows 7, I was able to install without any problem, SAP GUI 7.20, TrendMicro antivirus. There is embeded Windows Defender in Windows 8, but it has to be switched off to let Trend to run.
The magic is unlocked when you have real "METRO" app in hand. Then Windows 8 (with WinRT) will shine differently. As you know, WinRT gives an asyncronous framework for fluid interface, it is more secure, as it run apps in isolated enviroment where not all user right are immediately given to an app, etc, etc.