Why would that surprise anyone? Anyone that knows anything about Casey knows that he wants to be Governor above anything else. Senator for life? Please. That's probably the last thing Casey wants. Don't expect the guy to serve more than two terms there. Hell, plenty of people think that he won't run for a second term.
Ok, granted you know significantly more about Pennsylvania politics than I do, but wouldn't it be more prudent to wait for a variety of reasons? Do you think Casey could break the curse and keep the seat from flipping over to the Republicans in 2010; or actually unseat an incumbent governor in 2014? No one knows what the atmosphere will be like in the next mid-term elections, and it could be bad for Pennsylvania Democrats, depending on how Rendell goes out of office.