I would rather have Defender and Avast or AVG Free version over paying anything for Norton or McAfee. They catch less then the free softwares.
But seriously, that is silly. If other anti-virus software developers are able to get their stuff working in Vista/Win7 with leaving defender on that it cant be that tough for Norton/McAffee to do it as well. That is just laziness and waning the people to go byu their standards than to actually do something useful for their users.
Defernder is a great utility. It doesnt just stop spyware, it also can help you find problems, troubleshoot issues with your PC among other things. So this is nothing but a epic fail for both of those companies and just shows how much of a fail it truly is.