For a company on the whole who touts "Free maintenance" on their cars for 4 years/50k they are expecting that their used cars have a much better reliability than those brands who do not offer such service.
Its possible that the individual dealerships can undermine the whole 'feature' or whatever you want to call what BMW is trying to accomplish by not providing the correct maintenance on the vehicles. There will always be a few bad apples but on the most part, why would a dealership not do the work when they are getting reimbursed from BMW? To save a few bucks on each oil change? Sounds silly.