Not necessarily. I know two people who play on the Boston style, and one who plays on the Philharmonic. Headjoints are such a personal thing that it really does not matter which is more favorable. It is possible that one of the newer styles is a replacement for the Boston, but I have no idea if this is true. This is often the case with companies who change things around for marketing purposes. Again, I do not know if this is the case here, just a thought.[/b]
Powell no longer makes the Boston cut, just the other three. The Venti cut is the newest I think, but it certainly isn't a replacement for the Boston (the Venti style has quite a high riser which plays very loud but with less flexibility).
fluttiegurl is right--it's all about marketing. I think they like to introduce something new every so often, so they quit making whatever old styles are less popular. Every headjoint is different though, even within the same style/cut, so you really have to evaluate headjoints on an individual basis.