No it's the diff between 4 years and 5 years. 5 year contracts are limited now-a-days.
I think the trade was good for every party involved. Houston is taking some big risks, much more than OKC. They're banking a lot on Harden and Lin, which might pay off in the long run, but as I rarely watch them, I can't say I know a lot more about their roster. I don't think Lin is overrated (unless someone is calling him the next Nash or something). I suspect Houston is going to try to create a mini Wade/James setup since they are both ball handlers.
Does Houston have any good bigs? I would LOVE to see the Rockets eclipse the Mavs this season