If they insist on giving a shit about their economy, trait refunds are the wrong place to target anyway; all that the fee is going to do is encourage people to follow guides that other players have written instead of learning and experimenting for themselves (and that's going to be a problem even if respecs are completely free, so I don't know why they'd want to exacerbate the situation).
If they want to take a significant amount of money out of the economy, they should be taking a percentage out of every transaction that goes on in the auction house - and if they already are doing that, then they should just increase the percentage fee until it's at the level they want.
At least if you want to avoid participating in a gold sink that revolves around the auction house, you need to take the time to arrange buying and selling over some external auction site/forum (which is much less convenient than the AH, and requires that you personally invest time in setting up the deal - time that you could have used to make more money had you gone with the automated AH solution). Avoiding a respec cost is as simple as sticking to whatever cookie cutter 'build guides' happen to be in vogue, and never straying from them.
The auction house and probably the in-game mail system are good choices for tuning outbound gold. Between that and the crafting/durability costs, you should be able to get to whatever levels you need to keep reasonable pressure applied. You could also do something like applying a small fee for stuff like creating custom titles, some guild-related customization functions, things like that. There's enough opportunities there that it makes the use of a gold fee on the traits seem like a really odd choice. I wonder what their intent is.
Edit - Reading yesterday's post on the official blog, I read this:
After a character has spent their trait points, they can visit a trainer to reset their traits and refund their previously spent points for a small fee.
We realized that an important part of building a character is some sense of permanence. With this new system, you are flexible enough to change if you really want to, but you should still feel like the choices you made matter while you are out adventuring or slogging your way through a dungeon. In competitive PvP, you have a separately saved trait build and can respec free of charge.
I don't know, I can't help but feel there's not much sense of permanence in a system where there's only a "small fee" involved with changing it, much less one where you are completely free from that restriction in one section of the game.