Fortunately, I've never had any such problems on award stays. Marriott has treated me the same as if I was doing a normal revenue stay - as a Gold, that usually includes some sort of upgrade or desirable room (high floor, good view, lounge access, etc.), with my room preferences met. That has always included adjoining rooms when I've requested it.

The experience you had is unacceptable. It sounds like laziness on the part of the hotel: you showed up late, so they had reassigned your rooms to someone else. Then they decided to hold the fact that you were using points against you in hopes that you'd say "Oh, OK, I should just be happy with a 'free' room." As you correctly point out, there are no "free" rooms. Every Marriott point is paid for and accounted for when it is "minted". You paid for them in one form or another. By treating you badly on the award stay, they only diminish your perceived value of the points, which is bad for Marriott in the long run.