The only time I have come against this was on a certificate upgrade from DFW-YYZ. Somehow they screwed up (I think they were delayed and in a hurry and did not fully load the plane) and did not have enough meals, period, for the J cabin. I was informed that since I was an upgrade (albeit AP Elite) I probably would not get the meal but could still have one of the meals sold in coach gratis. I had a Latitude fare and by that point (last year) I think all Latitudes were getting those meals free in coach anyway.

It did not bother me in any case, since the Swiss Chalet chipotle chicken wrap I had was more to my taste than the J meals that day. . . .

I think what anoys most people is the point from the previous post: that in most cases it is more or less arbitrary rather than a predicatiable, set policy.