There was clearly a lot of support for Kara and Artem from the pros and the other celebrities before the final. There are several possible reasons for this, the most obvious one (Occam's Razor) being that the consensus of opinion is that they were the better dancers and deserved to win.
That's particularly likely for the pros, who are unlikely to give a toss about 'journeys', or whether they have fond memories of Blue Peter; they would be more inclined to make a judgement based on pure dancing ability because that's their own area of expertise. I don't think many would deny that Kara is the best technician among the celebs.
But, if you'll forgive me coming over all Doctor Pam, I think there might be a psychological reason why Kara's fellow celeb contestants favoured her. They were all (with the exception of Pamela) eliminated by a combination of judges' votes and public vote. Their own self-esteem would require them, however subconsciously, to want to believe they had been eliminated not because the public didn't like them, but because their dancing wasn't up to standard (not their fault, in other words). Therefore, they would have a greater respect for good dancing rather than 'niceness' in order to justify their own elimination. The only exception to this is Widdy, who has made no secret about her preference for Matt, but the only reason she stayed in for so long was because of public support, so she is psychologically bound to think that popularity is more important than dancing ability.
Btw, I read that Gavin has said in other media that he wanted Kara to win, but was 'pressured' by the BBC to support Matt publicly on TV.