I'm shocked that Mashable is perceived to be 8x the value TechCrunch was, when it was acquired by AOL. Either TechCrunch was low-balled, or Mashable's value is over-inflated. I suspect the latter...
Mashable has a wider audience, less niche (startups are not mainstream yet). Mashable also has a higher traffic rate. Pete Cashmore knows what he's doing.