I dunno. I think Paradox makes a pretty good work with updates and patches...
At least my opinion is that AI has improved more or less in every update they have made.
Example AI doesn't make "suicide" landings so often as it used to be in orginal HoI.
And I have understood that most of the players in their forums are quite satisfied with HoI and it's improvements. And community has also made many mods that also gives some extra challenge.
And talking about talking about game interface and mechanism, I'm quite sure Paradox uses the same mechanics only because it's one of the reasons why their games are so popular. Why to chance a working consept? It could be worse!
Again, I hope you understand what I'm saying.