This weeks Blog Azeroth Shared topic was from Ringo Flinthammer from Flinthammer Hall (Link is in the blog roll).
For the first time, WoW’s latest expansion, Cataclysm, only raised the level cap by 5 levels, in addition to the other content it added. Was Blizzard right to make this call? All other things being equal — the same number of high level zones and dungeons, for instance — should they have raised the cap by 10 levels? Should the fourth expansion be a 5-level or 10-level jump?
1. In my opinion, levels are just fillers. There are 3 parts to this game. Questing, Raiding and PvP. Regardless of what the levels are for the expansion there are still new quests / new lore to be explored.
2. The difference between this expansion and the last expansions levels were very different. Tackling 60-70 or 70-80 wasn’t as daunting as 80-85 was. With millions of experience points needed to level it felt impossible.
3. I heard a little rumor that Blizzards wants to stop at level 100 so if you divide 20 levels by 10 levels you only get 2 expansions. If you divide 20 levels by 5 levels however you get 4 expansions. (Again this is a rumor).
4. The amount of content they included in Cataclysm far surpasses those extra five levels.
5. For all those altoholics who had 10 level 80’s getting those 5 levels on all of them is enough work.
Yeah I know short but sweet in my opinion.
Bag Overflow 
I agree. The cooperative nature of the game really doesn’t begin until you are at max level. It seems the expansions require additional levels only to get players familiar with the new zones. I felt the new zones in this last expansion were fun to level through, and quite different than previous zones.