It's the nature of the game. SWC is being played in real time - meaning that the game moves on even if you're not online. The extended time frame here - taking hours to move from one end of the city to another, for example - is meant to sort of accommodate your offline hours. It gives less of an advantage to those guys who can afford to stay online 24/7. That's my take, anyway.
And, well, it [i]makes[/i] sense. I'd expect a city to be large - consider how much of a planet's surface it takes up.