There are far more differences than that. Ignoring each's individual flavor and different people's personal preferences, there are still differences that can be quantified using objective criteria much as
AAA or Mobile or the unofficial guide might use. Simply using rack rates is a fairly representative method unto itself which likely mirror's other rating methods. I know there are those out there that would like to think them all equal other than personal preference and it simply isn't true.
The point was they separate out the villas from the deluxe hotels and put them into their own category.