They say the list is the most popular extensions by category. RES is in the productivity category and presumably was omitted in favor of the 10 extensions in that category with 10M+ users. And productivity is the largest category so there are probably dozens more in the gap between 10M+ and 2.2M.
Yes, and since we don't have data past 10M installs for any given extension, all of those are essentially tied for the top spot.
The top list lists only the top extension in that category.