The AH is important in both games, and D3 received a huge critic from everyone because of it, even when the GOLD AH had less problems than the GW2 AH is having.
Hacving said this, i dont bash the developers, i know they are probably working on it, i know its not the only thing they have to worry about and i know it was a hard to test feature because they needed tons of players trying to use it to stress test it.
But the AH is still down after more than 4 days, and there is nothing wrong in complaining about it, as long as its a respectfull complaint.