Doing what it says on the tin

During the launch of yesterday's midterm review (notice how the words pile up with so little meaning), David Cameron described the coalition as 'a Ronseal deal. It does what it says on the tin'. There are so many grounds for objecting to this (there never was a tin, for example, figurative or otherwise), but what struck me was the explanation.
The phrase 'does (exactly) what it says on the tin' has been used in Ronseal adverts since 1994 and  figuratively in other contexts since 1997. I've just does a search in the Guardian (1995-2012) and there are over 300 examples. Normal people use it in normal life too -- all the time. It's in the OED. It's perfectly unremarkable in British English to say that something (anything) does what it says on the tin. So Cameron, or his speechwriters, decided to use it to signal that he's a down-to-earth kind of a bloke who likes nothing better than a weekend trip to B&Q. Unfortunately, they blew it by providing the unnecessary explanation. Or perhaps it's more sinister. What's really odd is the inclusion of the brand-name: that's what the phrase is explaining here. So maybe this is actually an example of product placement: got to pay for those tax cuts somehow! Either way, twat moment carefully avoided, Dave. Well done mate. Lol.