3e is RM translated to a d20. DC's are how RM has always worked. Routine mnv, 3 or higher, easy, 5 or higher, light, 6 or higher, medium, 10 or higher, etc. RM instead uses a table, but the 3e mechanic is certainly the same.
That's not a new idea, it's how Armour Class has always worked in D&D. Shadowrun had target numbers, too (although had dice pools as well). In fact, Rolemaster's distinguishing factor on skills, I'd say, is partial success, which in general 3.x doesn't have (other than in diplomacy, although it does have gradations of failure in other skills like climb).
Skills are also a direct copy of RM in 3e. Professions have a set of skills that are cheap, while all other skills cost twice as much to develop. Simplified certainly, but obviously an idea out of RM.
Actually, Runequest/BRP skill improvements are easier to learn if you have talent in that general area (although not by the same amount as in RM or D&D); it's older than RM and doesn't have classes or levels (but in the sense of D&D classes, Rolemaster doesn't have them either), but the idea of differentiated skill costs doesn't come from RM. Skills are hardly the major element of 3.x in any case; 1e had non-weapon proficiencies and 3.x skills are pretty simply viewed, I think, as an extension of that.
By the time 3.x was released, there was a bunch of thinking about rpg design by a host of people.
DnD did what RM should have done in 92-93, created a simplified version of its rule core that any 11 yr old could learn easily without fear of intimidation.
I think that most people don't find the 3.x core terribly simple and I would say with good reason, it isn't; it's also more complicated than the 2e and 1e core (although 2e as a whole got fairly complex, given all the extra crunch supplements). Indeed, I think that RM2 is simpler but relies more on GM interpretation (as does RMSS).
The big deals with 3.x in terms of changes are things like the tactical combat/action economy, the new multiclassing, a bunch of regularisation as with statuses and bonuses and spell descriptions, plus the xp progression, etc.
Playing 3.x, in my opinion and (now somewhat extensive) experience doesn't feel remotely like playing RM.
