Current microprocessors are very complex beasts. To develop an high-performance CPU architecture, you not only need many very smart engineers, but much time (3-5 years) and money (in the order of billions $$$). Moreover, bleeding-edge fabrication plants are incredibly expensive, and they must be continuously upgraded to newer process technologies.
So, it is perfectly understandable that both AMD and Intel (the two main x86 players) try to differentiate they offer, selling processors that spans from 50$ to ~1000$, a range of about 20X. While they want to sell you the most high-price (and high-margin) processors, they also realize that, as the market is very cost-sensitive, the bulk of R&D and production costs must be spread over a very large, low-profit product base. On top of that, all their processors must perform at least decently, or user will loudly complain (hello, Atom users!).