Perhaps it's because of - as mentioned before - my lack of interest in it.
A lack of interest is irrelevant. Sherlock Holmes is so famous and such an important and influential part of literary history it's almost impossible to avoid absorbing some basic knowledge about it from the world around you without even activley looking to find out stuff about it.
For example, I have zero interest in The Beetles. I've never listened to a record by the band or any of the individual member's solo efforts. I've never intentionally sought out any information about them. But yet I can still name every single member as well as name some of their albums. Because it's practically impossible to not know. I'd have to have put actual effort into not knowing.
I'm not saying you should have any interest in Sherlock Holmes, either the new TV serious or the original stories. But I am genuinely suprised you didn't know John Watson's name. Maybe it's just because I'm from the UK, I dunno.
Edit: Also, Cumberbach is hardly what most people would consider a "pretty boy", at least not in the typical usage of the term. He's rather odd looking, even people who fancy him (and I'm sure there's no shortage) would probably concede that he's a little bit odd looking and not conventionally "pretty".
