Not unbelievable to me at all. The NRSC always supports incumbent Republicans over challengers, no matter how liberal the incumbent is. This is business as usual for them, and they've done even worse. You should have seen the disgusting anti-Laffey ads they ran in RI to support ultra-liberal Lincoln Chafee (who had a voted record to the LEFT of Russ Feingold!) At least they're not spending conservative money to run anti-Toomey ads... not yet anyway. Bottom line, though, never donate $$$ to an "official" GOP organization like the NRSC or the RNC. If you're going to donate money, always give to individual candidates instead.
I mentioned this on a previous thread on this subject; but, the NRSC did this the last time Toomey challenged Specter. Same old, same old. The only hope is a strong grass-roots movement to work tirelessly for Toomey. (And, get people to support Toomey with their $'s and not send them to the NRSC.)