Yes, it's the screw that varies the spring tension in the derailleur's top pivot. It adjusts the amount of deraileur rotation about the top pivot, allowing adjustment of chain gap and large cog clearance.

I strong suspect, based on the emoticon, that rootboy's comment was made in jest. He's been around long enough to know what a B-tension screw is, though he may have no experience with one. It's quite possible that all his bicycle's pre-date this feature. A lot of these C&V guys get stuck in their ways and just aren't capable of understanding any of the newer technology.