Why are all modern sport bikes wet sump designs, as opposed to dry sump? Seems like dry sumps (which are used in high performance and racings cars) would be the more "stable" way to lubricate a high performance engine, especially one whose attitude (leaning left/right) changes quite a lot. Don't have to worry about the crank getting bogged down in the oil, or whipping it into a froth, thus creating a problem with oil pressure. Even my old CB750 had a dry sump system.
ALL modern sport bikes DO NOT use wet-sump oiling, as you infer.
Most Aprilia motorcycles use dry-sump oiling, as well as the KTM Super Duke and 1190 RC-8.
Other sportbikes, the names of which you would recognize, use dry-sump oiling systems - I just can't think of any more examples right now.
I would agree with Blu that the reason is probably cost...the Japanese OEMs are trying to maintain a certain price point in their bikes as one of the ways to differentiate them from the European bikes.
A hallmark of Jap bikes has always been the ability to equal or exceed the performance of Euro bikes, at a lower price of admission. Part of the reason they are able to do this is by limiting unnecessary gadgets on the bikes (such as dry-sump oiling).
Yes, dry-sump offers some advantages, such as lower weight and consistent oiling in high-G cornering, but it's really not needed - these bikes do fine with wet-sump.