At the risk of sounding offensive (well actually not really) - well like, for American cartoons I think it's common practice to hire white actors to play white people, Asians to play Asians and black people to play black people, right? Obviously it's a whole different situation in Japan, so I don't think it's weird for us to find it more natural for series with non-Asian people, or where the general population would speak English, to be dubbed in English. In the same way it's probably pretty convincing over in Japan when Japanese people try to play non-Japanese parts, but it doesn't seem right over here because we know what person of x nationality sounds like, in general.
But on the other hand, all those old kung-fu movies don't seem natural when they're dubbed, even if the actors are Chinese/Japanese/whatever. Because there's no reason they'd just happen to be speaking English/etc.
I was wondering if there are parts of Europe where you it's hard to find some random ethnic type, unlike in the US, so when the dub calls for it (let's say, a Russian dub of Afro Samurai), do they ever have to fake it?
By the way, hiring random celebrities as VAs is not the answer:
http://www.youtube.com/watch?v=6Bih4x51zRA