Only if you have enough surface area, which is not always the case, especially in the early eras (Forests, hills etc) and cavalary is usually worth it as well (1-2 Units). Some cities on Civ 5 cannot be taken early because of the surrounding Terrain and because it would funel your army in such a way that you'd simply loose. Even this aspect is completely missing in MUPT a la Civ4. My handling of Civ4 Sods was merely mechanical - you didn't have to react to anything but another sod (if there even was one - most of the time the AI was waiting inside the City, which is iornically exactly the place where Units were the most vulnerable). Atleast in Civ 5 I have to think some things through before attacking.