So if the Foundation isn't interested in suing them to enforce it, then we're not left with anything that can be sued against. The *community* is hardly likely to instigate a lawsuit against Answers.com for what... breach of contract maybe?
What would the Foundation sue for? The foundation doesn't own the copyright. Only the authors can sue, and I expect they could in this case: Answers.com doesn't seem to be following the license.
In practice, however, I expect the only times anyone would sue for not following the GFDL is either if they really didn't like the person doing it (or what they were doing with it) and it was just a way to stop them, or if they had modified the content and not released their modifications under a free license and someone had a problem with that on ideological grounds (or, they simply liked the modifications and wanted to use them). No one is likely to sue for simple copying, but that doesn't make it any more legal.