People also have to consider that in many, many instances we currently have, if a dps has high enough ilvl and the healer does as well, if a very low ilvl tank dies, there may be certain times (% till boss death, trash clear, etc.) where the healer can just keep everyone alive and cure themselves and the dps who has to tank effectively enough to avoid a complete wipe. I have done this numerous times either keeping myself alive long enough for trash to die (after getting aggro w/ Holy), or to keep a random high ilvl dps alive long enough for a boss clear. Given with how much we are overgeared, keeping myself (6200 or so HP on WHM with food) and a similarly geared but not max ilvl dps alive for a boss kill is easy. This is when the tank may be new and have sub ilvl 100-110 gear, etc.
Again, the issue is overgearing - not bad dungeon design. When looking at design, we must consider the ivl the dungeons were made to be completed with. As many have said, experts are boringly easy because we're all 30+ ilvls over what they are made for...