The "Second Half Player" Fallacy

In a recent podcast, a fantasy baseball "expert" was discussing the expected rebound of certain alleged "second half" players. The podcaster listed certain pitchers that he thought would have second half rebounds. Why am I mentioning this as a fallacy?? Well, maybe it is true in some instances, but here, specifically are the players mentioned by this podcaster:

Matt Cain, Erik Bedard, Kelvim Escobar, Jon Garland, Joe Nathan, Francisco Cordero, Francisco Rodriguez.

These are all very talented pitchers; with the possible exception of Garland all have tremendous skills that needn't be addressed here; we all know them. The premise of the podcast was that these were all "second half" players, because they all performed appreciably better in the second half last year. Do you see the problem here?

Just to look at one or two here (since the point is easily made) here is a look at Joe Nathan. As I am writing this he has a 2.59 ERA, 1.40 WHIP, 14 Saves. Presumably the podcaster was looking at that WHIP and relatively meager save total. So, he said that he felt Joe Nathan would rebound in the second half, since he has a history of "second half rebounds." However, the podcaster only mentioned the 2006 season. So let's even assume that there was a "history." Will this be the driving force behind any second half improvement?

Nathan has a 38% hit rate, which is astoundingly high for a pitcher of his caliber. Even for a pedestrian pitcher we would expect a regression to the mean of 30% on a going forward basis. Nathan has, in his career, never allowed a BABIP of more than .300, yet now he is close to .390. If he improves will it be because he is a "second half player?"