Universal Dock Model Number

I have just purchased an Apple Universal Dock (with remote), to be used to connect my Nano (and soon iPhone 3G) to a pair of Audioengine A5 active speakers.

The dock I've purchased has a model number MB125G/ A.
Browsing the net, I've found the Universal Dock with model number MB125G/ B.

Any body know the difference between the A and the B model?

I've tried phoning Apple tech. support but they couldn't answer the question.
I just want to make sure that I've not just purchased an out-of-date model.