I think the protection of PC protagonism is one of the 4e objectives/themes/characteristics that gives rise to the "easy mode" complaint.
I can see that. But I also tend to agree with [MENTION=82106]AbdulAlhazred[/MENTION] - more below.
Not having played 4e with the DMG2 available, this may be different now, but I felt it went a little too far in "protecting the PC protagonism". At times, I felt like the only things up for grabs were exactly how a fight progressed in X's and O's terms. Which, for me, isn't exactly compelling narrative.
Especially since low Heroic I have very rarely used a combat encounter at or less than the PCs' level - typically only if they are out of dailies, very low on surges, etc - in which case even modest encounters can matter. Otherwise I mostly use level+2 to level+5 combat encounters, with at-level skill challenges of varying degrees of complexity bridging between them.
But the moving Xs and Os is also, in my view, about the story dimension to encounters. And the only 4e book to really address that is the Worlds & Monsters preview, and there only in part (namely, story role of various monsters). It's a big gap in both DMGs (the DMG2 in particular insists that encounters, especially skill challenges, have story signficance, but says amost nothing about how to achieve this).
********
In my session last Sunday, the PCs had no daily powers left; the fighter and drow sorcerer were both on single-digit hit points with no surges; the wizard was just bloodied with 1 surge left; the paladin, the ranger-cleric and the CON elementalist sorcerer were OK on hp; but only the paladin had an action point.
They were moving through the Underdark hoping to avoid Torog crashing it down upon them (a skill challenge). I wanted a confrontation with The Cringe (18th elite brute Exarch of Torog) and some Wrackspawn minions (19th level brute minions). Because the PCs were successful on a group Stealth check moving through the Underdark after successfully taking down, rather deftly, a Wrackspawn scout, I let them get the benefit of surprise on The Cringe and entourage: they came to an escarpment and could hear, and then see when the looked over, The Cringe and 6 Wrackspawn standing at the bottom of it.
The PCs debated turning back and going down a side passage, but decided in the end to proceed ahead on The King's Highway (because Torog gave this part of the Underdark stability with his own blood, he can't just crash it down at will). So they planned a stealth assault from the lip of the escarpment.
The encounter I've described is an 18th level elite plus 6 19th level minions: 7600 XP, or level 15 for 6 PCs. The PCs themselves were 19th level. So this should have been a walkover. And in a purely mechanical sense it was, but the actual resolution was still quite interesting - because of their weakened state, so many of the PCs were no prepared to risk being attacked, and when the paladin eventually made his way down the escarpment to confront the NPCs he lost more than 100 hp in a single round and was restrained by The Cringe. If The Cringe had got another round of actions, he would have simply run away with the paladin (a special ability - drag restrained target at full speed without needing to check) - and even though it didn't actually happen, it created a tension in the situation that the players and I enjoyed. The PCs also were able to take down a fleeing Wrackspawn and thereby ensure that no messages were conveyed (manually, at least) to any other servants of Torog. More tension created and resolved.
Once they won the fight, the PCs were then able to make it safely back to the duergar hold that is their current base of operations - this required only a few minutes of narration.
Anyway, this is a pretty simple example, but I'm using it to try and illustrate (i) how even very simple story elements matter to an encounter - in this case, its place in the culmination of the skill challenge and hence the attemt to get home safely; and (ii) how even a very low level encounter (4 levels below the party!) can, in the right circumstances, pose a challenge.