Agree.
I have a hunch that one of the reasons linux desktop users aren't more heavily targeted by malware coders (aside from the different architecture), is that so many of them simply refuse to install anything from outside the repositories that it just isn't worth the trouble, and I say let's keep it that way.
Anyway, why would you need to? The only thing I have installed on this machine that didn't come with the Ubuntu CD is Clamtk, from the repositories. Everything else I need is there already.
Seems a shame for companies like avast who are trying to provide a service I know - perhaps reputable security tools are a reasonable exception.