Yeah you are absolutely right there. David already stated that the construction costs of commercial buildings would be adjusted if this was to be implemented due to this concern. Also, this feature would only apply to commercial buildings since they take into account distance to the CBD. Otherwise, the player could in fact pop appartments everywhere on the map and put his/her own retail stores within (thus replacing all standard retail stores). Let's say that these typically have luxurious halls on the bottom floor instead to make them more attractive.
Still, as you said, profits with commercial buildings are made way too easy. You can simply build a dozen of these, come back years later and yet find them highly profitable without much effort. Although, with higher construction costs (which in my opinion would be more realistic), since the return on initial investment will take longer, the player that has limited money at a certain time might hesitate before spending in real estate in front of other options (like investing in the stock exchange instead) even though he/she could take advantage of the retail store as you mentioned. One's commerical buildings will definitely be profitable some day, but they are sure not the best option for the player that seeks the fastest growth.
