Hey, it's not as if the White Stripes and Raconteurs are dead or anything like that. The White Stripes released Icky Thump in 2007 and have another one coming out later in 2009.
The Raconteurs pushed out Consolers of the Lonely just last year. He's been overlapping the two bands and he's clearly capable of adding a third...why shouldn't he? If you like Jack but don't want to listen to The Dead Weather, pop in one of his other albums, I don't see the cause for displeasure here.
Besides, don't you get the feeling that The Dead Weather is just a side project that will last a couple of years? It's a supergroup amalgam, an experiment consisting of 4 members that all have allegiances to other bands. Not generally the kind of thing that lasts, unless they hit it huge. The point is, he's not abandoning The White Stripes if that's your concern.
And I wasn't trying to equate him with Clapton, that'd be ridiculous. My point was that Clapton dabbled in a myriad of other groups and never lost his essential sound. Neither will Jack.