Leonel, at first I had the same thought, but then I realized it's actually not that far-fetched. First, remember that they have to be only one or two tiles away (and not even the diagonal 2) from a core city to be worked (and therefore grow), so that growth limit would be a lot of coding for very little impact.
Second, it's actually not unrealistic for a "suburb" to spring up away from the city (i.e, a farm tile in between or something.) I see two situations where that'd happen:
1> When the town and the city were connected by a major transportation line, whether it's a trade route, railroad, river, or highway. In modern times, it's easy to live in a "rural" town and commute to the city, which is the justification I was using for the production bonus in the first place.
2> When two cities grew near each other, close enough that you wouldn't (or couldn't) put them as overlapping Civ4 cities but far enough that one isn't considered an actual suburb of the other. American examples of this would be Baltimore-Washington D.C., Los Angeles-San Diego, or Seattle-Tacoma. Sure, one might be larger than the other, but it's not the same thing.
And, if you're going to say that Suburbs should only give benefits to the core city if they're contiguous, why aren't cottages/hamlets/villages/towns limited that way?
Anyway,
