I have noticed this game plays quite differently with 3 or 4 players.
With 3 there is more space per person, so you'll be spending more on roads and houses, with 4 there is less space, so cities and development cards are more popular.
True that you have more space - but to counter that you will receive fewer resources and less opportunity to trade.
Also note that by using some of the expansions you can create larger worlds - in which case 4 players may have even more space then 3 players.
Settlers is not just a single game - it is a game system!