Yeah—because we all know that wealth indicates intelligence. /sarc
You can't found a company like Microsoft from scratch, build it into the world's biggest software company and hold that position for for decades, and in the process become the world's richest man for 14 straight years, and America's richest man for even longer, in a super competitive business like technology, by being a dumbass. You need plenty of smarts, determination, grit etc.
Looking down the Frobes 400 list of the richest Americans(and leaving out those who inherited their wealth), I can't see even one person at the higher echelons of that list, who I will not consider pretty smart.
http://www.forbes.com/forbes-400/
If you think its so easy, try making a billion, and see where you get.