The original Sport came with the chopped carry handle style sights. Most people wanted folding sights over those, and the Magpul folding rear sight was cheaper too, so S&W changed them. Do you think it affected the MSRP? It didn't.

The Sport II, equipped with the MBUS rear sight is equipped the way an entry level rifle should be, ready to fire out of the box. Removing that sight would have minimal, if any effect on the price of the rifle, especially if the price continues downward. And the newbies that the rifle is marketed and priced for don't know what they really want yet.

If you want a S&W M&P 15 rifle that you choose what sights you would like to put on it, S&W has you covered with the M&P 15 OR.