This is fundamentally true, but I don't think the situation is as simple as that. Without getting into the nitty gritty of it, it seems to me that rolling friction involved in the use of a rim drive trainer wouldn't cause any more brake track wear than regular braking. I also think the mechanical properties of the materials of the two parts in contact must be considered. The resistance wheels on the trainer I bought my friend seem to be made of a fairly pliable rubber or urethane which I think would wear out before the aluminum in the brake track (which is likely surface treated to provide better wear resistance) did. A good analog is that of a tire drive trainer. Over a long enough time period for significant wear to occur, does the tire or the drum wear out first? Granted the drum likely isn't aluminum, but the basic principle is the same.

I dunno, this is all supposition without any data to back it up, but it makes sense to me. I'm sure there are plenty of great tire drive trainers out there which don't chew up tires when used properly, but that's not to say that the rim drive concept is fundamentally flawed and that "somebody with a brain" should throw theirs in the trash and run to the LBS to spend cash on a tire drive.