Well, there is a difference and there isn't a difference obviously. Seems like there's all kinds of opinions. However, I can say that SOMETIMES, there is a difference in what they sell to the public, In my example- the Callaway Diablo Octane standard driver varies from the Octane Diablo TOUR or (TP designation as it sometimes advertised). I know because I HAVE the "TOUR" model. In comparison to the STANDARD model, the face of the club is a *bit* deeper, the head is fractionally shallower and more of the classic teardrop shape (because the club is taller the material is moved around) and the shaft is 1/2" SHORTER (45-1/2 as opposed to 46"). A quick look and you would never see a difference. There are reasons for this but I wont go into the picayune details about why it works for me.
Now- that is a "Tour" (or TP) version.. FOR THE MASSES. The "Tour ISSUE" clubs are likely custom cast to that pros specs, with swing weights, face angles, lie angles, etc... all designed in conjunction with the specific shaft and grip they might use. And just because you can buy a "tour issue" head doesn't mean it will work anything LIKE it would if the actual Pro used it. To be honest it would probably be a great waste of money to put a $700 head on a $35 shaft with a $2 grip.