First paragraph seems like an acknowledgement by Blizz that having all pally/shammy buffs stacking would be a little overpowered.
We plan to allow most of the Shaman and Paladin buff effects to stack, with a few exceptions of course. This means that both will be extremely useful in regards to improving the potential power level of those around them. Be careful not to think in current "WoW" terms and only digest current end-game. When the Burning Crusade releases all classes will have access to new spells, talents and abilities, which will be taken advantage of (and play a large part in) grouping/raiding in the expansion's end-game.
It's also important to note that moving forward, we'll be able to design our raid and dungeon encounters to specifically draw out the strengths of each of these classes, whereas now we actually take measures to prevent an encounter from being too beneficial to only one of the classes.
We'd also like to mention that beyond raiding, we think it will be exciting for players who feel strong allegiance to one specific faction to have access to a class that has seemed unavailable to them.
Second perhaps addresses concerns that most encounters are too warrior-reliant
What really gets me going is this mention of a 'previously unavailable class' in the third.