It's what they do nowadays--cluster computing--faster and cheaper than the big Kluges of the past because they can do it with off the shelf parts, and easy to expand and upgrade--System X, "the world's most powerful and cheapest homebuilt supercomputer." was the third fastest computer in the world when it went online in 2003, and it consisted of about 1100 off the shelf Mac G5s.
They do it because they got tired of investing hundreds of millions of dollars in machines that were obsolete they day were completed--