It's not that the site itself accepts BTC or not. It matters if the people selling things on the site accept BTC.  On this site you will be sure to be willing to accept bitcoins (since that's the point of the site).  On craigslist, odds are that at least today, 99.99% of the people will people you might want to deal with will not even know what bitcoins are.

In a couple years if bitcoins become more mainstream, we won't need this site anymore and can all just use craigslist and other normal sites.  But today, I think this will help people connect.