what's the percentange of 4 player games that use more then 4 buttons?
Zero, both the D&D games have 4 buttons, not more than 4.
Also, when going by sort info for that sort of thing you are going to get an extreme amount of bad data. Many driving games are listed as having crazy amounts of buttons due to things like 4-way shifters being counted as 4 buttons all by themselves. Other anomolies are of course the quiz and Mahjong games, and "no joystick" all button games, which often had 5, but can be played with 3 if you use a joystick instead of left-right buttons.
Stargate and Defender both technically have a buttload of buttons, but have 4 or less if you are playing them with an 8-way (they then only have fire, smart bomb, hyperspace, and then Stargate has Inviso). Same for Asteroids, Asteroids Deluxe, and many other similar games.
Basically the only REAL games with more than four buttons are.
Mortal Kombat series.
The expanded Streetfighter series (including Marvel Vs. Capcom, etc).
Time Killers and a few other obscure fighters.
I mean you could TRY to include Mahjong and quiz support, but then you would need 20+ buttons per player, or something else equally rediculous.