Why couldn't he pitch like that for the Sox? (part 2)

By now, all Sox fans probably know how John Smoltz has been tearing it up for the St. Louis Cardinals. He's not the only reclamation project the Sox tried this year.

After a rocky April, Brad Penny seemed to get into a groove, and by the end of May had a 5-1 won-loss record. He got even better in June, allowing only 11 runs in 5 starts, giving him a 3.17 ERA for the month. Despite throwing 6 innings of shutout ball on July 24th, his ERA for July nearly doubled over the previous month. August was even worse, 8.31 ERA.

The experiment didn't work for this NL pitcher, either, so the Sox let him go. What does he go out and do? After signing with the SF Giants, he pitched 8.1 innings of shutout ball against Philadephia, allowing only 5 hits, 1 walk, and 2 strikeouts.

Did the Sox let him go too early? Or is he just another NL pitcher that can't handle AL lumber?