Which may very well be how Marriott's inventory system treats them, but if you check out Platinum Benefits, note that it specifically excludes "upgrades from studio to 1- or 2-bedrooms". I do believe that sometime in the past, this same site stated that upgrades from a studio to a 1-bedroom suite" were a part of the program. But even the existing text implies that going from a studio to a 1-bedroom suite would be an "upgrade".

Also note that the 48 hour room Guarantee is applicable at RIs for studio suites only, not 1 bedroom or 2 bedroom suites. So somehow Marriott has a distinction between them.

But per this thread, if upgrades to suites (i.e. 1 or 2 bedroom suite) at an RI are not part of the MR program, is it acceptable for a specific hotel to use rate or someother criteria for their own personal hotel upgrade process?

Or if there are more Gold/Plat elites than upgradeable rooms, is it acceptable for a hotel to use their own internal upgrade ordering process (i.e. rate)?