In my humble opinion, it was a problem in earlier games as well.When I saying specific I mean much more specific and stable than what you had in BG. Milestone specific: clearing the guards of a gate (that will always have to be there to defend the gate even if you killed them the last time. Since combats in 4e are more complicated and beg for more variety, having to repeat the same combats -on the same disposition of terrain, etch- would be a problem IMO.
Its not realistic for the guards to just keep coming back as you just keep slaughtering them. And its annoying to go through the same fight for no apparent gain, especially if the combat system isn't incredibly interesting, and the game is designed to not permit XP farming.
Its the old "boredom as punishment" trick, and I hate it. "Play in the way I say you should, or else you'll have to replay the same fight over and over for no gain, without advancing the plot."
Its almost as horrible as requiring people to reload from saving checkpoints, so that when you die fighting the boss, you have to repeat the whole level over again just to get a second chance in the final battle.