Then it changed to lvl 95 or 97 or 242. Dosen't change the fact that 1, You can give your heroic/normal/flexx weapon right away after it dropped to your other lvl 90 alt, before logging in with him.
2, If they wanted nothing else, but this, it would have been "Bind on Account" purple, like the new store helms. The fact that it is heirloom, means you can use it for leveling. We already have weapons for 1-8x, the only logical explanation remains, it will scale upwards while leveling for next expansion. Which is a genius idea, if you think about. Your hard earned weapon won't be useless on lvl 91 with the first blue.