well the way that it works in Grunt is actually that you have your source branch and then there is a separate build branch -- so the source is still versioned, but only the artifacts from the "build" branch are presented to public / pushed to your server, whatever.
i just appreciate the security builds add. In enterprise coding the paradigm is very simple -- pretty much keep whatever u want in source, but only built artifacts are ever deployed to the servers. In a closed-source setting this is perfect.
I understand what you mean though it doesn't really solve the issue of distributed, open-source development. (I guess no one would really make a public repo unless they wanted to share, huh?)
This doesn't at all solve the OP's problem, you shouldn't be putting your build under source control in lieu of your source code.