This has been suggested in the past. I seem to recall that Jens didn't like the idea because the support questions would come back to him, and possibly reflect badly on his product.
When you control the entire board, you have control over Quality Assurance.
When you provide just a socket, the customer could put in fake, damaged or just plain wrong chips, and he'd still have to provide support - and if he didn't then it would look bad for him.
That's why there's not a socket version, and to be honest it makes sense to me. Keeping a good rep is hard enough, let alone when people are fitting their own CPUs....
