I spoke with representatives of three oil filters at the AIMExpo out of curiosity about the change from concave to convex bottoms. What I heard was that one company makes the base plates for a number of filter companies. They'd had some complaints about how hard it was to get filters to thread on some cars, where the filter is hard to get to. Their answer was to change to the convex (sticking out) style because it makes it easier to get the first thread on. What they had not counted on were other users where the little change can affect sealing - like us!!!
Apparently, some of the filter makers have insisted that the vendor return to the concave bases, which just muddies the water even more. Hopefully over time the filter companies will settle on one or the other design and the currently mixed stock will be cleared out. In the meantime, if your favorite brand didn't go to the convex you should be fine.