Sorry for the newb question folks. I'm a 1911 guy who just got in on this HK hoopla! Thanks for your help!

Yes.

Thanks!

FYI:
All USP mags within caliber fit all versions (USP, Tac, Elite, Expert, Match).
Compact mags fit only the Compact and the P2K/SK.  The Compact and the P2K (US version) use the same mags.  Compact .357 and Compact .40 mags are the same.  There are two verisons of each which may mislead you into thinking there are slight differences (a cut out in the feed lip), but in fact HK changed the mags in both calibers a while back.
P2KSK mags will only fit the SK (too short to fit anything else).
Socom mags will fit and function perfectly in the USP .45.
USP mags will not work in the SOCOM, even if the baseplates are swapped so they will lock in the Mk 23 they will not feed reliably ( USP mags have shorter feed lips than SOCOM mags).
P7-M8 mags only fit the P7-M8
P7 (PSP) mags only fit the P7 (PSP)

I wonder why regular USP mags wont fit the mk23? You would think it would lower HKs production cost and the interchangeability would be an additional benefit for buyers getting the mk23...

They fit if you change the floor plate to the SOCOM style but they still won't function well.  The shorter feed lips on the USP mags causes feeding problems in the SOCOM.  For some reason the longer feed lips used on the SOCOM mags work perfectly in the USP, so to me that begs the question why not make all of them with the longer feed lips???  Only HK can answer that question.