I'm not sure blueprint clearances are tighter but generally operating (at temperature) clearences are. So in that respect I'd be a little surprised if build tolerences are that much tighter. If you notice a lot of newer motors are pretty noisy (the GM LS motors especially) when they're cold. Plus add the fact that most motors run 5W and some even 0W oils so somethings got to be up. Most motors these days run at 192 degrees and some over 200. The main benefit of modern motors is the fuel injection which minimizes fuel wash and greatly enhance bore and ring longevity.

I suspect coatings are more for protecting internal parts under extreme (hot or cold) start conditions than any real MPG savings, the gains at cruising speeds would be relatively infintesimal(sp?) compared to the bang for the buck gains of optimizing fuel mapping at cruising speeds