First off, the players don't always know that they're going to walk into a boss battle, so they might not have necessarily rested.
Fourth edition was designed for the players to fight more encounters in a day than previous one. The concept of fighting one tough battle, resting, then fighting another one, takes away the dailies and healing surge management aspect. If the players are going through hordes of enemies to go slay the evil Orc general, they'll have to choose whether or not to use their daily powers and action points on this tough Goblin Lieutenant or save it for Lord Orking Facesmasher. It would be anti-climatic, to say the least, for them to leave for 6 hours then come back like you would in a JRPG.
GMs who feel throwing same level enemies to their players isn't enough of a challenge need to have them fighting more than just one encounter. Perhaps you can also have them gain bonus XP for each additional encounter they face before resting, or simply have a roleplay reason why they can't simply rest anywhere at any time.
I'm speaking only from a point of view of the mechanics as I'm not much into encounter heavy games, partly because of this:
Two days agos, my group resumed our 4E campaign (which we had taken a 5 months break from) and as we rotate GM, the GM of the day was the ultimate Dungeon Master. This guy, regardless of the story, will find a way to add a dungeon anywhere and anytime, while we two other GMs, do more roleplay-oriented games.
He has the exact same problem described above. Since he finds normal encounters too easy, he throws up to lvl 14 monsters at our lvl 6 group. The thing with lvl 10+ monsters is that they have +20 attack bonus against my AC 24 paladin. Themselves have AC 27, which my +11 Attack bonus has a hard time hitting. Thus, they hit us all the time and we waste most of our encounters and dailies. It says something about fourth edition that we're able to kill them at all, but we could easily get wiped if the dices don't roll our ways. I believe it is poor GMing to have a fight rely solely on luck instead of tactics. We did tell him and he will try to adjust, but the best way to teach is by example so next game, I'll do what I never do: a actual dungeon.