I don't think that most of you understand that this is a Marketing Information device, just like airline frequent flyer schemes.
All the hotels I've ever worked in operate on a minimum of 300% mark up on food and beverage (and sometimes more) so not only are they still making money when you eat there, it is seen as a bonus (as an earlier poster mentioned) as you may not otherwise have eaten there. On top of that, an extra 2 covers in the restaurant means that fixed costs go down per meal, and these is less wastage and spoilage in the kitchen
What Accor gets in return is detailed information about the travel habits and spending habits of the most valuable market segment to them. At one time, the average spend per head of the loyalty club member was nearly twice that of the leisure traveller
Accor run it as a stand alone company (and when it is generating that kind of data and market intelligence, it really only has to break even) and just like any other hotel booking agency such as wotif, expedia etc they receive an allocation of rooms from individual hotels in the group. The number they receive will depend on the individual managers of the hotel.
My boss is still a member of Advantage Plus and uses it on a regular basis, but understand the full picture before you hand over money. You are agreeing to pay them some money and give them your travel, spending and contact data, and they are foregoing some of the profit they would otherwise have made (which they recoup by way of your membership fee). Simple contract really.