Usually I like to see the contestants exit the show in order of talent (or lack thereof), just because I find the worst dancers a bit embarrassing and awkward to watch, and I feel a sense of 'fair play' towards the ones who are clearly better.
However, in John's case I genuinely do enjoy his dances with Kristina (undoubtedly all down to Kristina's skill and John's basic sense of rhythm), and not because they are 'comedy gold' - that sack-of-spuds paso drag notwithstanding. I enjoy them far more than I've enjoyed the dances of the departed contestants.
It wouldn't bother me if John lasted another week at the expense of Heather (yes, I know she's nice and a better dancer, but I enjoy J&C's routines more than H&B's). After that it gets harder and I think I'd rather watch the others more than John. For me, that's why he's still there. He and Kristina are entertaining to watch; he's got a good attitude; he's light on his feet and - to a non-dancer like me - looks actually quite good at the ballroom.