You still can. Follow the same directions you wrote, but instead of clicking on Songs, click on the little "Show All" link on the top right of the Songs search results. Then you can sort by popularity etc.
EDIT: No, actually, I think you're right. You can *view* the popularity that way, but I don't think you can sort by it anymore. Weird.
EDIT 2: Ok, if you click the band name, you'll get a list of Albums and Songs, which are sorted by "Bestsellers" by default. So I think that's what you're looking for.