Typically, AI designers cheat by:-
1) Shorter build times
2) Allowing the AI to ignore the tech tree and build things without regard to the prerequisites
3) Giving the AI discounts on purchase prices.
4) Letting the AI see everything
I think the C&C RA AI does 1, 3 & 4. It's simpler than doing anything more comprehensive, but to be fair remember the AI is the last thing developed for a game and is probably thrown together in a few weeks. We started a decade down the line with the benefit of knowing how best to play the game in terms of strategies and then spent literially years on and off fine tuning our scripts for the AI. (and mostly off, given it was done an hour here and there when people could be assed in spare time in an evening)
Biting the hand that feeds IT
