I have to agree with why wouldn't they just spend a bit of time making it compatable, I have checked and Norton is also uncompatable with defender. Companys of the scale of Mcafee and Norton have huge resources and it would take no time for them to make it compatable, but my problem is the way they make it difficult to stop the messages. It doesn't stop your pc from running but it is just a pain and all you get when you look for help is being told to uninstall defender which you cant actualy do as its part of the os. There is another way you can stop it but I fogot how to do it but you have to go somewhere and check a few boxes.
I have just had a look on the web and the problem is with MS not Norton or McAfee. They are claiming that MS wont give them the program code so they can make their software compatable so they can get an advantage over them in the security market. Here is the link:
Symantec: Microsoft won't give us key Vista tech - CNET News