When someone says "both x but also y ..." I feel that it is worse than a slip. It seems like deliberate hype: the speaker feels, perhaps only half-consciously, that ordinary language is inadequate.*** In the same way that satisfactory is just not good enough and that even good is not satisfactory - all must be outstanding nowadays - "both ... and" simply doesn't do it any more.
Doesn't this show, though, an insensitivity (and even insensibility) both to normal phrases but also to the way the language works, or used to?
Did that sentence seem ok? Weren't you expecting a sort of addition and reinforcement, agreement even, after "both"? An "and", in fact? (A lot of people wouldn't understand what I'm going on about by now.)
"Both" talks about two things, not more, and is not, or was not, normally followed by the contrast or disagreement shown by "but". (That is not to say that it didn't allow a semantic contrast, of course, eg "both light and dark".)
Does anyone else feel almost hurt every time they hear this? It is not like most grammatical slips, often caused by insecurity, but more like a blow to the guts of the language. And something rather representative of the hype and falsity of a lot of life in 2013.
***Of course, this may not always be true. Some deliberate use by influential speakers in the media may be copied, consciously or unconsciously or somewhere in between. Distinguished sociolinguists may well tell me I am wrong on this, or, at least, that there is no evidence for imitation of the media at all. Please do and discuss it here.