Headshots aren't that easy, still takes skill.
Yeah I've got watches and flare guns and all kinds of stuff, but no bow.
When the trading system comes in that will be much better, you can trade for what you want.
If you could trade then that's better than achievements, achievements should be for things like the hats, to show off how good you are but you don't have to be a TF2 god just to get one of the weapons unlocks.