Tbh, I was never overly impressed with him on the show but there's no denying his success. I'd agree with a lot of the comments made. Vocally, he's not the best but he's good enough and they've found a sound that suits him, his voice and his personality. The new single is really good, IMO. Might not win any Ivor Novello's but it's catchy and great fun.
And that's where his personality comes into it - image in music isn't always about being sexy (Olly's not ugly but he's not Brad Pitt). It's about matching (and selling) the music. Hence why Susan Boyle can make millions singing Christmas carols and about her long lost dreams. Adele sells millions, but if she started releasing Rihanna's songs, she'd flop because people wouldn't buy into the whole package. Likewise, Rihanna singing Christmas carols wouldn't work. It's also where they're losing it with Leona.
I think coming off a strong first album but not one which was massive has helped. Xtra Factor probably helps but that's just reflective of the fact that he does seem to put himself out there as much as possible.
He has a great public image for a solo male off X Factor - not too dull and boring (Leon/Joe) but not spouting the kind of angsty wannabe credible crap of Cardle. Seems to be hugely unpopular on DS - which might be a good sign!