Well I'll tell you this much. As the manager of a shop that sells iPod related stuff, I'm desperate for a new connector.
Why? No one buys speaker docks any more. Everyone's got one. They only buy a new one to upgrade or if theirs breaks. It's a saturated market.
New connector, new custom for me.
That's business. Apple will of course be seeing licensing money from every single one of them. I'm sure they have other reasons, space being primary (a lot of their proprietary connectors are purely for space, see Mini Displayport for example), but I'm sure they won't mind the extra money generated from sales of docks.