The thing is, that most people in the general public have no idea what .ws, .info, and .biz domains are. So, marketing is not that great for these guys. I mean, the .net's are hard enough for people.
Until the general public becomes more familiar with domain names and the internet, the dot com is probably the best way to go.
As for resale value, I dont see much value in any domains off the .com and .net.