One fact that I don't think anyone has brought up is that the metal portions of the frame on the .357 version are made of steel (blackened stainless I believe), where as the metal portions of the frame on the .38 version are an alluminum alloy. I heard a story a while back (I believe it was on THR) that a steady diet of .38+P's in the .38 version will lead to frame warping on the .38 version due to the materials used. This was however a case of something like 10,000 + hot loads, and who would do that anyway? This is a defense revolver, not a plinker. However, if I am going to make the leap into poly revolvers, I want all the strength I can get in the metal parts.
For me, it's the .357 model with the intent that I shoot .38's for practice, and 38+P's for defense. Having the .357 model will give me peace of mind that my investment is not going to "wear out" when off course all guns do wear out eventually.