And the other major change in 4e - it's harder to house rule, at least "officially". There is no real official forum for how to make changes to the rules, and that's a situation that has never really occurred previously.
OTOH, 4E is the most friendly edition to
successfully house rule without help, in that it frequently tells you why things are the way they are--the famous transparency.
But mainly, I don't think you can say any edition (or most any system) is easier or harder to house rule, as a whole. It very much depends on what you want to do.
If I want to make a new class, you can't get much easier than Basic, whereas 4E is a nightmare (assuming I want to make the class print out like the official ones). If I want to change how skills work while maintaining the existing balance, 3E is a nightmare (very embedded in the system in surprising ways), 4E is somewhat easier, NWP is very easy, and in Basic it is either relatively hard (make up my own system) or not applicable.
In 4E, I can say that, "All skill checks made in a scene, with the same intent, by the same character, take a cumulative +5 to the DC." This is a very narrow but sharp house rule in 4E, almost surgical, but with wide-ranging implications. Yet, it is so transparent to our group, that it took me all of 2 minutes to introduce it, and they immediately grasped the implications and were able to intelligently decide whether to try it or not. A new Basic class is similarly easy to grasp, but not really at all the same in its effect on the game.