Though you don't have to, Alchenar. There is an option - as Lieste said - to use figurative symbols. Many people seem to do that (not me, as it happens) judging from the AARs, and that seems fine to me. After all, the NATO symbols aren't historically accurate either ( like Rockin Harry, would love to see all those terribly complicated historical Axis symbols used, myself!). All these options are different to having little 3D icons though. Can't see the point of that, at this scale, as everyone has said. It would make it look like a toy. It's certainly a game where - as Brindlebane hinted - your imagination needs to wake up and do the work and if you're looking for eye candy you'll be disappointed. I think it's a bit of an aquired taste, to be honest - but once the bug bites, once you get it, then you might find it hard to put up with other games that lack the superb concept and amazing AI.
The point isn't historical accuracy - the point is to have a set of readily identifiable symbols that broadly identify whichever white box you happen to be looking at on the screen; NATO symbols are what everyone uses, they're a good system, and once you learn them you'll never forget them. That makes them the best choice.
While 3d Icons might work for other games where hexes and units are of consistent size, they can't work here on a map that's entirely 2d and where units can vary greatly in footprint over the course of a game - it would just be confusing and misleading.