Duc is NOT competitive at this point
If you read the rule books carefully, you will find that in AMA and WSB twins have fewer modification restrictions than 4-cyl bikes, meaning that racing teams on ducatis can (and probably do) modify their bikes more to be able to run with the japs. In pure HP terms, the ducs have been behind the ball since the late 80's.
Their MotoGP bike has been running on 4 cylinders for a couple of years now. Ducati announced the 4 cyl bike for sale maybe one or two years ago, i.e. it was supposed to be available...maybe '07 or '08 (not sure the date they set for that...).... . In any case, even ducati is now going with the 4 cyl. It has a lot to do with hp, and also emissions. Ducati has a huge following in europe, and the euro emission standards have always been more stringent than US standards (including California!). 4's tend to run cleaner, i.e. less waste during the combustion cycle. This directly relates to power as well. It just makes plain old horse-sense....