So because Tavares did it, everyone can?
Rob Schremp was never able to add a step. Adam Almqvist was never able to improve his skating enough at his size to make it. That's just off the top of my head, and I am sure there are others who have not been able to make the improvement.
Did they not try hard enough? Or did their genetics not allow it? I mean, how do we really know the answer to that? I have to believe some people are just slow, and can't get much faster. And some people are weak, and can't get much stronger.
Edit: In doing some googling, I found a book on the subject and ordered it. If anyone is interested may want to scope it out:
http://thesportsgene.com (it's also on Amazon)
Here is an excerpt:
That excerpt is about endurance, but I believe the same principles would also apply towards speed and strength.