Imagine the grind if you are F2P and want the top-level airship. Even if Astral Diamonds are 1 per TP, that is still 3850 Turbine Points.
Ai yi yi.
Now speculate further: If Astral Diamonds bind-to-account, someone would have to individally pony up 3850 of them.
Wouldn't that stretch the "100% F2P" too far to remain credible? 99.999% F2P is still pretty good, even if not as catchy a slogan, and if my speculations pan out it is also way more honest.
p.s. If I am wrong and this thread causes a ruckus, I will personally host a server-wide event to balance my karma