There was nothing special with maven-war-plugin execution, it was just declared, no special configuration, just plain default execution.
I'm not sure, but as far as I can remember there were no quickfixes available, nothing special/related was in logs, and plugin was installed. Will try again.
Btw, here is link to this broken eclipse bundle/installation: http://dl.dropbox.com/u/11530426/eclipse-3.7-SR2-Full--broken.zip (~600MB)
The problem markers you refer to about "execution context not covered" should have a quick fix available offering to search/download the proper integration plugin.
I know it sucks but does the same problem occur if you simply just install Beta1 directly without doing an update ?
Upgrading from milestones to beta1 should work, but we did do some feature reorgs for Beta which might make such update fail.