2K8, I’m sure, lets you pick the location of pitches, but I haven’t bothered to find out how that’s done yet. The catcher puts up the mitt, you throw to the mitt with the pitch it selects for you. I assume that as difficulty gets harder, it doesn’t tell you what pitch to throw. I like it, though, mostly because of the gesture controls. If you throw a crappy pitch, it’ll get hit. If you throw a crappy pitch to a good hitter, it’s gone.
MLB 08 allows you to turn on or off a feature (I forget the exact name at the moment) where your catcher will suggest pitches and pitch location for you based on the batter and his hot zones. You can choose to ignore the suggestions (you’ll actually see the pitcher “shake-off” the suggestion) if you want. In addition, '08 allows you to see what your pitcher has thrown to the batter previously in the at-bat, during previous at-bats, or to any other batter in the game (and under a wide variety of circumstances).
And yes, the AI seems pretty good when it comes to changing up your pitches. Throwing the same pitch to the same location two or three times in a row is almost a guarantee that you’re going to get hit.
Based on what you’ve said, I can’t understand at all why you wouldn’t want to use the RTTS mode to create your own pitcher, but perhaps I’m misunderstanding what you’re after.