I did technician work as a side job during college. It seemed like most dorms had data closets every floor/every other floor. Some buildings only had them in the attic and basement, but they were also usually limited to 4 levels. Are most large apartment buildings similar?
Does it really matter if there are comms closets nearby though?
It wouldn't surprise me if fiber optic cable was cheaper than cat6 to buy in bulk (Copper is expensive, and the process to manufacture the copper cables is more complex), and if you're doing fiber to the building anyway, you still end up with a media converter - so there is likely no significant cost saving there either.
It may actually be higher cost to have a centralised (within the building) media converter - ports need to be provisioned for the max possible customers up front. The class of hardware will likely be different too - matching enterprise style datacenter hardware, instead of the cheap and easy to replace stuff they send to customers...
This was 10 years ago, but the data closets had SFPs on the switches for the fiber. So the cost of the "media converter" was really low - just needed a few. There was existing CAT5 in the walls, all of the runs would be well less than 100 m which is why I brought up the comm closets. For a new builds, I have no idea for the cost difference. But for the insane number of buildings wired with CAT5/CAT5e/CAT6, this solution works well. Trying to pull fiber to replace CAT5 (as in without removing the drywall) would be very expensive and likely to damage the fiber.
