TripAdvisor and Expedia share common ownership, and as such have a vested interest in not alienating the major chains from which they derive a good deal of income. I have noticed a perceptible increase in positive ratings for many of the branded properties in major markets, less so in secondary or tertiary areas. Perhaps this is due to major franchisors improving their quality control programs to counteract today's instant dissemination of information technologies that have the capability of making negative occurances go viral (e.g. bedbug photos).
My personal belief is that impartiality takes a backseat to revenue.