I dont agree with the initial post, though im not in any way against it
Basically, I think they asked Alesha back because she is the defending champion and Jill because she is probably one of the best dancer's they have had regardless of what people say.
Inviting Kelly back was a nice touch. She may not have been able to carry on competing, but there is absolutely no doubt she would have been in the final if she had carried on - even though she was in the bottom 2 just before she left, the judges adored her and would have carried her through regardless ala Snowdon.
I suppose theres an argument for saying they expected Austin to be in the final so got three girls back, but then again, im sure it would have been very easy for them to 'drop' one of the girls for a male celebrity from yesteryear - Karen and Flavia were free, so they could have gotten Mark and Matt. Lol