The dangers of weak random numbers

What I don't understand is why hardware RNGs aren't more common.  A number of embedded CPUs
contain them, but not the bulk of mainstream CPUs.  They take up so little silicon compared to
everything else, and provide such high quality results that they really ought to be
ubiquitous. 

Sure, if you introduced them on mainstream CPUs today, it'd still be 5 years before they were
everywhere, so you'd still have to implement other techniques in the meantime.  But, those
could be a bridge to a better overall solution rather than a road to more hand wringing in 5
or 10 years when somebody finds the next weakness.