I assumed that the bigger bottles were for exec rooms or junior suites or suites. I've stayed at some properties that offered a higher end set of toiletries (L'Occitane, Penhaligons) for some of the better rooms & the more mundane toiletries (Aromatherapy, Thann) for regular rooms. Even w/ some of the higher end toiletries, depending on the room (or more accurately suite), the toiletry sizes were bigger.

Cheers.