Providing your defense skill-ups aren't lagging terribly, it's effectively 4 levels.
[So not the defense cap, but rather keeping up with your defense skill]
If they were for some reason... say you played a Holy Pally through a chunk of levelling and turned tank... you probably would want to AoE grind some grey/greenies for awhile to get your Def up to drop some ouch.
That stat seems to keep up rather well though, I think you'd almost have to go out of your way not to have it reasonable. But you could see where Paladins and Druids playing healer/caster roles converting to do some tanking probably want to take a look and maybe have to skill it up a bit.
Sometimes getting beat on is the solution
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