The troll is a good example because it's a soldier(soldiers being the worst case in many instances) and still 6 levels higher than the party. If you think pc's can't handle this encounter you clearly haven't played the game enough. It's got a 25 reflex. 8th level rogues will hit this on about 10, a 7 with combat advantage which they will be working diligently to get. The troll doesn't have a lot of hit points for a 14th level critter but it does have regen. Drop a flaming sphere next to the troll and he's crippled, and coupled with just a few rounds of attention from the rogue this creature will likely perish.
So, as long as the group has a dagger based rogue, and a wizard, and someone to flank wth the rogue it should be fine. Not only does each member of the party have to be optimized ... the actual choice of characters has to be optimized as well. Whether or not the troll is going to be a huge threat or a manageable one is based not just on how optimized the party is, but exactly what classes are there. So ... you should know what your party can handle before you throw just ANY "balanced" encounter against them.
The trolls AC is very daunting but after a few swings the party will know this and the fighter will definitely go elsewhere with his attacks, on the other hand many of his powers have the reliable keyword so he can keep working with the rogue to grant CA which also ups his chances to hit to 13-15.
In your numbers you failed to account for weapon proficiency. Expect about an 11 ATT bonus at 8th level add 4 more for a rogue with dagger and 3 or 4 more for a fighter with his weapon of choice. Nimble blade is +1 with CA so the rogue might have a 18 ATT bonus on combat advantage attacks (he has a couple powers that guarantee at least 1-2 flanking opportunities a combat and the party supplies the rest). I think a 7 to hit with something like Walking Wounded (+ sneak dmg) is pretty powerful. a 5 to hit if the cleric lands a lance of faith on him first.
Again ... so long as the group has a rogue, it will be fine. "Having a rogue in the party" should not be a requirement for having a balanced party.
The rest of the encounter is still pretty powerful. 5 level 9 creatures but all of them are easily hit by the party. This is no cake walk but the reason it's so challenging is that the bad guys are a level 11 encounter not that they included the wartroll. N+3 = hard. The troll doesn't break the encounter and asserting it does only demonstrates a lack of understanding how the game works. The beauty of this design is that they've actually taken the time to figure out exactly how much the party can take and created both the experience point budget and the two ranges. One for overall encounter difficulty n-2 to n+4 and one for individual threats L-4 to L+7. These three numbers allow the dm to be extremely creative in designing NON-homogeneous groups and therefore extremely interesting and unique encounters. As you decrease the ranges you cut back on choices and flavor. Removing the granularity from the game is not good.
A DM needs to know their party. They need to know that when you go to the top levels of encounter design it's assuming that the entire party is AT LEAST at the baseline of being optimal, and that this means that many in the party are only going to be hitting maybe 30% of the time unless they can get bonuses, or attack the right defense, etc. If they know that there are PCs that are not "at their best", they need to recognise that and adjust accordingly.
The players and the DM are all playing the same game. If their expectations are not synced up it doesn't matter which one is playing the game wrong. What is important is that they resolve their issue.
The beauty of D&D is that there is more than one way to play it. You CAN have extremely difficult encounter to challenge people who want to have difficult and potentially deadly encounters and test their abilities to build characters able to withstand them. It's
also possible for players to try less than optimal ideas (such as race/class combinations that don't yield optimal builds) and for the DM to cut out the most dangerous encounters because the players have increased the difficulty by reducing PC optimization.
The problem comes when PC goals and DM goals, or goals between different PCs, are not synced up. As has been said in the thread, the problem with the feat is if only some of the players take it. The feat is extremely good, and in most groups, everyone will eventually take it, some early in heroic tier, and some later in heroic. Any group that actually has an optimized character taking the feat, and an extremely unoptimized character not taking the feat (The example of the dwarf paladin with 16 charisma and the human fighter with 20 strength was made) is a group that has problems beyond the feat.
It's exactly because of the time and effort put into designing the monsters/experience budget/encounter ranges that the pc's need to do their part and be pretty close to the expected power level.
Because the designers made the game such that there is a very large range of possible encounters, it's their job to play the game correctly and have their PCs fit a narrow mold. If they don't optimize they are playing the game incorrectly and wasting the time of the designers ...
OR, the DM can take advantage of the wide design area and slowly test the boundaries of the party to see what is acceptable for them, not just what is acceptable for the expected power level. Some parties may not be able to take on level + 7 monsters. Also, some parties may be able to take one SOME, but not ALL level + 7 monsters. Guidelines help in encounter design. The statement has more to do with "don't even bother trying level + 8" so much as "you really
should try level + 7". If something is at the very top of the power level a party is expected to go up against, you don't just throw it out there without considering what your party can do. A good DM does more than just builds encounters for a party that is hypothetically at the expected power level, and throws it up against their party. Especially if the party has players that:
(a) don't know they are expected to be at a certain power level
(b) don't know what the expected power level is
(c) don't want to be confined by expected power level (race/class combination is particularly important, and multiclassing, especially paragon multiclassing, would be discouraged)
Problems arise from lack of communication about expectation. It's not about players doing it wrong because they haven't built characters capable of being as good as the hypothetical party (like not having a Rogue with the particular at-will power that targets reflex in order to have an easy time against the Troll, for example).