To be fair, banks may also be grossly overvalued. Their market valuations are entirely dependent on large government bailouts (although Wells Fargo was certainly in good shape relative to their peers in 08.)
> Their market valuations are entirely dependent on large government bailouts
Hasn't been the case for years (and I'm pretty sure it was never the case actually). They are valued by their assets (funds in accounts, real estate holdings, equity in companies/investments, etc). Facebook's valuation appears to be based on nothing but magic.