It's interesting to look outside the US, in countries where the D&D translations didn't come in a decade early: When facing Cthulhu, Paranoia, Rolemaster, Vampire and the like on an even playing field, D&D didn't really win.
And has now come full circle to be played at my table in the US. The new version (under the name Dragonbane for its English version) is published by Free League Publishing and is quite good.
The American market rules supreme. Any setting and/or ruleset popular with Americans will be able to afford much higher production values than its competitors. Those production values in turn attract non-American players.