For planets without starports, that simply means they can't BUILD ships, not that they can't offer logistical support to them. For underdeveloped planets, smaller ships could simply land to reprovision, and presumably larger ships would have shuttles or cargo lighters or something. For a current comparison, not every port has shipyards, but that doesn't mean they can't run a cargo terminal
While this is true, we're comparing real life to game mechanics here. If you want to compare, then, okay, a planet doesn't need to have a starport, but a ship needs to actually orbit the planet for a turn (or perhaps a "resupply move" which takes one of its moves away) in order to re-focus it's range on that planet.
I don't think that's going to happen, so making the starport requirement is more likely to work.
Plus, though it is in the game, Starport = shipyard as Port = (naval) shipyard. In other words, starports are really places for ships to land, they're only used in this game as places where ships are built.
Other TBS games I've played had similar mechanics to that, but with an additional problem - each ship/fleet could only go x# of turns without resupplying. If GalCiv went that way, actual distance wouldn't matter at all, only the number of turns that ship had been away from a planet. Not necessarily a bad way of doing things, but it would require a massive overhaul to implement.
Back to the point, though. You do realize that the AI builds a starport on every planet, right? Any limitation based on building starports will only serve to annoy the player, the AI will be entirely unaffected. Just like the suggested tech prereq for a colony module, this requirement would only slow down a colony rush a turn or two, unless you made starports ruinously expensive to rush-buy.
First off, the main thing that needs to go away is the unnoted range boost. If you build a ship and put no life support at all on it, it should basically be trapped on the planet you built it on, only able to travel a few parsecs away, not all the way to the next sector.
It's not really unnoted, it's a base component of the hull. Your basic hull provides minimal engines, life support, hit points (if applicable), and sensors - the same way the base colony building provides a baseline level of food, morale, manufacturing, and research capability. It's intended to provide the very basic necessities to make a functional unit.
At present, the basic range given by the base hull is scaled pretty severely with map size. I wouldn't mind if base range was cut maybe 10% for tiny/small maps, and then scaled up a bit for medium/large, and kept at that level for the bigger maps, along with Starstriker1's suggested tweek. It would address the issue in question, but not be game-breaking on small maps.
