Hey folks,  I just noticed something last night that I thought I should mention here:  Have any of you noticed your defensive rating stat seeming to be independant of your armor class?  I noticed this when I opened my inventory window and saw that with all the buffs I had (cleric and paladin) I had roughly 2200 armor class.  With this AC I had about 4400 defensive rating in tiger and harmoneous stance.  This is bad because with only my Aum Liat buff, I still have about 43-4400 defensive rating, though my armor class is only about 850ish.  With crane stance my defensive rating goes up to around 4650.

Also, another weird thing is that even though I've gotten several armor upgrades since then, I've had roughly 4000-4300 defensive rating since L25ish (I'm L36 now).

Has anyone else noticed this or am I just doin something wrong?

The Defense value dervied from your evasion, mitigation, spell avoidance and spell mitigation - not only your armour class. This includes bonuses and penalties from buffs, debuffs, stances and what-not.
Since these are level vs. level compared, having about the same simply means you've maintained the same quality of gear the last 10 levels. If it had gone up you would have (quite likely) gotten better gear, if it had gone down you would (quite likely again) have gotten lesser quality upgrades (even though they are statwise superior, they are not level-level superior that the stat is actually presenting).
Dexterity appears to get a diminishing return on your parry/dodge as you gain level aswell (well, since it appears to be based on how close you are to your cap rather than your actual stat - you simply need more and more dexterity each level or it'll trail after - an overbuffed/twinked level 20 character with 360 dexterity would quite likely have maximum parry/dodge/crit - but you will have about half of it with 360 dex at level 40).