What's the difference between the BitTorrent clients named "BitTorrent" and "µTorrent"?

A similar question was asked but never really addressed the question, I think in part because of confusing terminology. So to be very clear: what's the difference between the two BitTorrent clients, one named "BitTorrent" and the one named "µTorrent"?

They look to have identical UIs, right down to the same checkboxes in the preference dialogs. Why are there two programs with different names that appear to be identical? Is one superior to the other? Are they different in any way?

Thanks.

uTorrent is often regarded as one of the lightest weight, full featured clients for Windows.

BitTorrent is the mainline client. It is the baseline other clients are compared against, as it offers the official implementation of the BitTorrent protocol.

It should be noted (just looked this up) that BitTorrent is no longer developing the mainline client, and is using uTorrent. If the preferences are exactly the same this would be why.

BitTorrent purchased µTorrent so they are the same. At one point BitTorrent added some additional software that was not needed so I stick with µTorrent.

BitTorrent DNA(tm) http://www.bittorrent.com/dna?csrc=splash