Rolex Datejust proves a good investment

I recently was researching Rolex prices online. As I cross referenced several websites I noticed that the going rate for a once entry level stainless steel Rolex datejust with a fluted bezel and jubilee bracelet was now equal to several more desirable (in my opinion) sport models with the heavier oyster bracelets and more durable cases. This brings me to the question; Why have the Sport models such as Submariners, Explorer IIs, and Sea Dwellers not been given the same courtesy of inflation? Has the pricing structure at Rolex merely been dictated by the Marketing Departments theory on what is in? From what I gather the increasing cost of precious metals and unfavorable economic climate are to blame. Good for those who bought low. Bad for those who are planning any near future purchases.