I cannot blame the top player base for all choosing Dwarf. It has a lot of strong qualities. First off, the advantage of having a hybrid unit is self explanatory. Berserker unit scares away a lot of competition, great for the realm (it's also very cheap). Dwarf's main resource is Iron Ore, and once you get past the very difficult transition into an Iron Ore economy, it has more advantages. All gold races must designate part of their economy into improvements (diamonds), while Dwarf focuses all their economy into Iron Ore. Iron Ore for Dwarf is their improvements and military. This allows them the flexibility to invest if they cannot grow or train if they can grow (utilizing their entire economy in each case). That type of flexibility is hard for opponents to predict, so they must always assume the Dwarf trains (more of a meta game).
Something like that.
Sure, and also they have a higher imping efficiency than any other race, but more importantly, dorfs are FUN!