Except that newer sensors can, and often do, outresolve older lenses (which prompts one to upgrade his lenses too).Agree with you here. Lenses last the longest and price drops the least. Electronics updates all the time, including sensor, video codec, memory buffer , image processor. Interchangable lens makes sense because you can keep the lens investment and just upgrade the electronics. Now with Ricoh, if I invest in a 70-200 F2.8 IS type of lens, I have to throw away if I want a newer sensor ? I don't get it.
The Ricoh way, lens and sensor design can be optimized for each other (size, quality), as is possible with fixed lens cameras. You can have small zooms and fast primes in the same system.
Obviously, there has to be some advantage compared to purchasing multiple compact cameras. For instance, buying the camera and both modules shouldn't be more expensive than buying an LX3 and a DP2. Then it would start making sense. You'd only need one charger, one flash, one EVF. You'd only need to learn one camera.