If you look at the download page for Sql 2008 R2 CU 6, you’ll a choice of six different download packages all for your platform:
Whu? Actually it turns out that all but one of these are subset packages of the main hotfix, that you’d only need to apply if – say – you only wanted to patch PowerPivot or SQL Native Client, but you didn’t want to have to download the whole update*.
Quite why this isn’t deemed worth mentioning anywhere in the relevant knowledge base article or on the download page itself is beyond me, but fortunately I happened to stumble upon an article on the SQL CSS team blog that explained it all (after I’d already downloaded half of them) so now I know.
And now, so do you.
[*] Note the rules are different for Sql 2005 – you do have to download all of them. So no potential confusion there.