It seems sir that you fail to understand the premise of supply lines and supply ships.
Take enough supply ships, either protect them in a nearby friendly or neutral system, or take them with you.
If your not behind enemy lines you will be supplied by supply ships that flow along the trade lanes.
If you do not do this then yes you will run out of ammo.... the whole history of warfare is about supply lines. Generally those cut off from supply LOST! You get surrounded "you lose"! You raid to deep without enough supply and support "you lose"! Your empire does not have enough raw materials for ammunition "you lose"... historically some armies were better trained and equipped than their adversaries... but the enemy had more shere industrial and resource might. The better trained and equipped army won all its battles and then LOST the war.
In space I imagine that "hidden" supply bases would play a huge role. The history of warfare again is in part about ships re-supplying back at base or at a neutral port and heading out undetected again.
In short if we ignore supply lines then we assume each ship has generations of families and is self sustained in both energy and raw materials. In short each ship is its own world.
For one, maybe he just thinks that it wouldn't, say, add anything fun to the game.
However, your premise of supply lines is simply stupid. First off, yes, the history of warfare has, and will likely, played an important part in the likely continued future of large-scale conflicts.
Unfortunately, space warfare is drastically different from anything that has ever been done before. First off, just how do you propose to hide these supply bases, and keep your ships undetected? Because if you think that's actually possible, you have no concept of just what space is really like.
Space is dark, and cold, yes. Which is exactly the reason why it's a terrible place to hide. Because it's so dark and cold, it means that any ship operating at normal capabilities (i.e., keeping the crew from freezing/cooking to death, keeping the ship from crashing into some random planet, whatever) will be visible for a very long distance.
You due a maneuvering burn, you get spotted. Keep in mind that the Space Shuttle's main engines can be seen from very far away. As in, from beyond the orbit of Pluto far away. A ship in the asteroid belt could spot the Space Shuttle's maneuvering engines. And a puny ion drive puttering away at one one-thousandth of a gee could be seen from a distance equal to the average distance between the Earth and the Sun.
And really, "self-sustained" in energy isn't too hard. You need to burn very little nuclear fuel for a gigawatt of power, and a gigawatt is, on average, similar to what the usual nuclear plant produces, for many, many homes. And that's on fusion power. In fact, assuming I've done my math right, a deuterium-tritium fusion reactor with a 95% efficiency and producing 250 gigawatts requires a little less than 6,000 kilograms of nuclear fuel. For around sixty years of continuous operation.
Furthermore, it's not a stretch to think that these ships would be heavily automated, reducing crew requirements (actually, a realistic space warship would likely be entirely robotic. Cheaper that way.). A spaceship really is it's own little world, though you've made an enormous leap in logic going from "no supply lines" to "generations of families and self-sustained in energy/raw materials".
Additionally, space, being a 3D environment, more or less has no boundaries. It's nigh impossible to blockade a planet. A space station, sure, you could blockade that.
A station in orbit of a planet, not so much. Because that planet can have much bigger and more deadly guns than your spaceship ever could.
It's also not unreasonable to think that these ships are equipped with a small manufacturing facility (or at least the larger ones) to assemble replacement parts or machine new ones as needed.
I wonder, though, did you ever read or hear about the SpecOps units that helped to liberate Afghanistan from the Taliban? Because those guys were dropped deep in enemy territory with little to no logistics support. Sure, they probably got the occassional supply drop from across the border, but most of their supplies probably had to, *gasp*, be secured from local resources.
Probably the biggest thing you've ignored, however, is the fact that supply lines may very well be implemented in an extremely abstract way, or, *shock*, the devs didn't think it would be a fun mechanic. No matter what you say, if the devs don't think it would be fun, then it isn't going in.
Couldn't have said it better my self, Destraex. An excellent example of what you are saying is Hannibal losing to Rome in the First Punic War.
Except, of course, space warfare will be completely unrelated to the First Punic War. Or in any way resemble, the First Punic War.
It also doesn't help that Rome more-or-less had other advantages, like defending home turf, familiarity with the terrain, familiarity with the weather, not loosing a bunch of guys from going over some mountain pass, etc. etc.