I think Lucas is the master of making exposition as sweet and to the point as possible.
I also don't think he "explained" everything in the prequels. A lot of people think for example that Midichlorians was this huge peice of exposition, but it was far shorter than Yoda or Ben rambling on and on about the Force in the classic trilogy. I'm not putting the classic trilogy down, I happen to love that exposition. I just think it all comes down to wether or not you are being open minded about the prequels. If you are open minded then you can roll along with all the things the prequels introduce without rolling your eyes, but if you go in with the mindset that Lucas shouldn't be adding anything to what we had in the classic trilogy, then anything new that Lucas introduces suddenly becomes "uneccesary, pointless exposition".
I really think there is a bit of prequel discrimination at work behind a lot of the "Prequels Explain Too Much" argument.