I disagree with that, at least for TA & Spring, because instead the computer remove all the burden of having to handle the complex details with ruleboook, pencil and paper, so they can have alot more details and complexity, for instance factoring unit's acceleration, unit's gun-mouth position at the instant of fire, shot's 3D trajectories, and much finer "turns", and uhm well ok since I actually have very little idea of what's playing a true wargame is like, maybe I'm wrong, but at least I know that if we had to manualy compute all that is going on during a Spring's game, a 1 hour game would take years or something.
Spring actually simulates a lot of physical reality that wargames skip over. However, it skips a great deal that a typical wargame will cover in much more detail. For example, each unit in Spring is exactly like every other unit. While there are actually quite a few things that can now be modified, for a true wargame approach, so far as I know, nobody is taking advantage of that yet.
And there are a lot of things you can do in a wargame very easily, that are very, very difficult to realize (at least, in a way that players will respond to well) on a computer. For example, in Silent Dark, buildings are represented by a structure of their walls. If you want your troops to travel through the building by destroying the walls, there are well-defined rules for handling that- and it's very simple and logical. In a video game, the problems become very difficult- what's a "wall", and if you're only simulating it in 2D, but the rest of your gameworld is in 3D, then how do you handle that, in terms of both visuals and game logic?
What is easily described in maybe two paragraphs of text, and is easy to use in a wargame, is a massive enterprise on the computer. Now, are there a few computer games that handle a lot of this in really obscene detail? Sure- and they're all turn-based, just like wargames, so far as I know.
And the time scale is very, very different, because it's arbitrary. In a typical wargame, you're dealing with a battle that IRL would be over in less than half an hour (wargame simulation of it may take 1-4 or more, depending on the players and the rules) in Spring, to months in Spring (giant strategic battles). Not that Spring can't handle larger scales or whatever, it's just that typical RTS games handle things very differently.
Also... I've never seen a RTS besides Myth, that didn't feature spawning and faux-economic behavior. In a typical wargame, if it's present at all, it's almost always abstract logic- you establish factories here, allocated resources there, maintained a line of communication here, etc. In a RTS, almost all of this is literally depicted, mainly (I suspect) to keep bases more interesting-looking and less static than because there's any real need, from a game-design standpoint (contrast the much greater popularity of "harvest" games over OTA's static mine-based model- I suspect that's part of why they have been more popular).