I played travian a while. It's actually quite similary to ic, there also are races witch different abilities (speed, def, attack) difference is they have different units for every race. You also have to produce resources (on which you have to wait hours after a while in the game) and you have to save for your own infrajumps. After some time you will start colonists, to colonize new 'cities'(comparable to eships?!?). Like i said they have different units for every race, which are used to raid the enemy, or after a while destroy his buildings.
Actually pretty fun and addicting too.
Combine it with the fact you can (or maybe have to) buy gold (for real money) to make things go faster in the game, and you'll see why this game is so big as it is 
Another big advantage of Travian is you can plan things to a single second, as al your actions you make, have a timeframe in which they will be finished (hh:mm:ss).
On a side note there's no honor there too, people will sign naps through the game (and they will turn out to be worth jack shit) after which you are too far behind to really catch up. Hence i stopped playing =p.
This is not something to advertise travian, just to explain the formula of their success. So that some things possible implenting to our game, may actually get done.