Okay, so here's the most definitive confirmation of the storage on the Optimus G:
Quick Look: LG Optimus G on AT&T and Sprint - YouTube
So, ATT went the smart route with 16gb internal / micro SD slot.
Sprint opted to keep the phone exactly as the Korean version with 32gb / no micro SD slot.
Other than that, no removable battery for either. Glad the actual carrier models were confirmed early, so that I could have my mind set on my final 1 year upgrade device (Note 2 is the winner).