I find the same thing, Bette. 800-900 words was my standard in the early days, but now I tend to be in the 1300-1600 word bracket.
Part of it is a sense of confidence, I feel - less worried about boring readers and losing their attention. And also greater ambition to cover more angles and dive a little deeper.
I still don't ever see myself straying beyond the 10-minute boundary, if only because I very seldom click on a 10+ minute piece, unless I already know the writer, and know I am interested in the subject. It's too big a time commitment.
Crazy though that sounds. 10 minutes!