There is no way to get these forks updated, unless you email each one of the owners and ask them to update.
I don't think you need to be worried about outdated forks, though. Let me explain why.
For some background (though you probably know this), here is how forks accumulate: Whenever I send a pull request to a GitHub project, I first fork it, send the request, and then forget about my fork. I might never use the project sources again, so I don't ever repush to it, unless I send another pull request. As a result I now have something like 50 forks and counting lying around, none of which are up-to-date. I've never bothered to delete any of those, simply because there is no reason to.
Depending on their workflow, some people might fork-then-clone just in case they ever want to send a pull request, which is why it looks like "they just push the fork button".
As a result, all active projects have outdated forks accumulating: If you check the Rails forks, you'll find that pretty much all of them are out of date.
Because of that, when I browse GitHub I assume that other people's forks are generally just throwaway copies, rather than properly maintained projects. So if I see "forked from" at the top, I'll instantly go to the upstream. I don't think I've ever cloned from a fork, unless the upstream explicitly told me that development continues in the fork.
So to summarize: Don't be embarrassed at all those old versions of your software lying around. Nobody uses them anyway. Think of them as a badge of popularity for your project instead. ;-)