I'd think the relative stupidity in US is on about the same level as in any country.
Lets think about factors like:
-size of population
-political Influence
-economical Influence
-freedom of press, media
-freedom of individual people
-openness of the culture
-etc etc
The level of stupidity in any country actually increases, seemingly, as such factors go up, no? (you don't hear a lot of stupid anecdotes regarding North Korean people, should that mean they are smarter than most? or are they just silenced by an overpowering government, or what?)
And about Bush.. well, I'm not a fan of him, but if you look back in the history, its not like he'd be the only questionable leader any country has ever had.
Another thing, if you start to evaluate the smarts of the people according to their politicians, you need to bring into the equation the culture and history of that country as whole, because that is what molds the choices that are made by people today. I mean, they could be doing exactly what they want - not what you want.