I have nothing to back this up, but this may be a reason for the results.
It seems like a lot of players only play with cards up to set 10. Those people play fellowship, towers standard, towers block, and movie (King block is available but not really played).
The people that play sets 11 and up usually prefer expanded. Open, standard, war of the ring, and hunters are generally ignored.
This could mean that anyone who likes the higher sets will play expanded every time they are online. Those who enjoy sets 1-10 will play a larger variation of games when they log on.
That's an interesting theory! I'd be curious to see some more data on that one.
One thing that I would point out, other than Fellowship, Expanded, Movie, and Towers Standard, all the other formats on Gemp have exceedingly low percentages of games being played. For example, over the last 30 days, all the games played for all the other formats other than the top four only added up to 11% of the total games played. So, all the less popular formats
combined added up to less than the fourth most popular format (Towers Standard), which clocked in at 11.3%. So, there doesn't really seem to be all that much variation outside of the top four formats.
I know that I play a lot of fellowship, towers, and movie. With that being said, it would inflate expanded play percentage because only that format is being played by a number of people, whereas a larger group may enjoy sets 1-10 but play a bunch of different formats relatively equally. This would slow down the percentages growth.
Basically it takes a larger group to get the percentages higher because they spread their games over a wider variety of formats.
That is theoretically true... however, if this is a
popularity contest, the point is a bit moot; If you split your time between Fellowship, Towers, and Movie, then clearly none of those three really outshines the other two. You like them better than Expanded, but other than that, you like them all about the same. You don't like one in particular enough to play it a whole lot more than the others, so I'd say even if what you say is true, the statistics on games played are still reflecting the popularity of those formats. If (for example) Movie really deserved to be more popular than Expanded, then more people would be playing it more often, and not spending their valuable time playing other formats.
I'd further suggest that the Daily Tournaments for Fellowship and Movie tend to bolster the stats for those two formats, because they are natural draws for players. Expanded does not have Dailies.