There's no doubt that may very well be true, however I would instead suggest that by keeping the entire phone, front shroud, display, motherboard, frame, and software the same and simply creating a new back that would allow more space for a larger battery is the far more likely scenario. From the points of simplicity, research and development and design & engineering costs, and ultimately profitability it's the obvious choice.
Further evidence that points to this, and the very likely possibility that the MAXX was in the works from the VERY BEGINNING of the RAZR is the fact that both the HD Home Dock and Navigation Dock were designed with removable inserts that as the image below (and also likely the Navigation Dock) just so happens to be exactly the additional room needed to fit the MAXX.
Coincidence??? I think not.
Referring to virtually EVERY other recent iteration of a Droid phone model from Motorola, for instance the D1, D2, D2 Global, D3, D4, DX, DX2, Bionic, etc., from what I can gather they have all had different versions of the OS and one was not necessarily interchangeable with the other, and yet, the Droid RAZR MAXX is running the exact same OS as the Droid RAZR is currently updated to - out of the box, 6.11.748.XT912.Verizon.en.US, as well as all the other systems, including radios, webtop, Kernal, etc., and right down to the BUILD DATE!
This means when the RAZR gets an update to the OTA version of the leaked 6.12.173 (or whatever it'll be called at that time), that the update will likely get pushed to both RAZR's. This also means it's likely good news for the MAXX people that when ICS comes to the RAZR, its fatter twin brother will get to eat his proportionately sized share as well.