In skating flexibility per se isn't essential, it's what skaters and choreographers do with it. A beautiful spiral timed to coincide with an emotional peak in the music seems to make time stop. It's a moment of beauty and peace in a program that's otherwise crammed with complex athletic feats. The appeal is almost universal (apart from a few critics on skating boards ). And it can't be easy to do on ice or we would see a lot more perfect positions.
If that's all the skater can do, she's not a real skater, just an acrobat. So IMO flexibility is not necessary, it's just a very big plus.
I guess I'm one of the few who dislikes that move where Shiz sticks up her leg and lets go. To me that's just a show-off trick that schoolgirls everywhere do in their bedrooms. OK, I grant it's harder on ice, but the position per se is ugly, to me. It compares unfavorably to the comparable movement in ballet, where the dancers slowly unfurl their leg with the music as a peak moment in a pas de deux. Whereas the arabesque spiral in skating is like the ballet move, plus it flies across ice.
But I bow to her Ina Bauer.
ETA: I kinda hate to say it, but these flexi-moves are really only for women. It must be biological - a revelation of the crotch area to display fertility and desirability. It can't be coincidental that in ballet they usually come in the pas de deux.