Well Bob Rock who produced the black album, was more well known for producing bands like Bon Jovi, so it was obviously Lars' intention to make Metallica radio friendly, no matter what bullshit he has spouted over the years.

Megadeth, as you say, is a far superior band, but they never sold out!
Ok, they refined their sound as well, but unlike Metallica, Megadeth were already alot more melodic in their style, so it wasnt a big stretch for them when they did make a slight detour into radio land!

Through all his shit, and the odd weaker album, Dave Mustaine has always stayed true to his vision of Megadeth.

I will buy every studio album Megadeth releases, almost as soon as it comes out, but the only way I will buy new Metallica albums (just to complete the set) is if I can find them cheaper than a Snickers bar!