This is well known among the medical community. People who are homozygous for CCR5 mutations are immune to HIV. However, to perform a stem cell transplant is not a benign procedure and may place somebody at greater risk than HIV, believe it or not. People with HIV can live long, productive, happy lives without any sign of disease thanks to the antiretrovirals that we have today (assuming that they take the medications regularly). Stem cell transplants have the risk of graft versus host disease, a life threatening reaction, and require strict matching of a donor to a recipient. To find a donor who matches you is difficult; to find somebody with a CCR5 homozygous mutation who matches you is not a common thing at all.

The short answer is that we have therapy that may have more benefit and less risk.

That's not to say that the CCR5 receptor is not being investigated. Here is a list of all articles that cite the original article referring to the "berlin patient." 74 articles in a little more than a year is pretty substantial.

http://scholar.google.com/scholar?start=10&hl=en&as_sdt=40000005&sciodt=40000000&cites=3571305302489850955