It's not that it's a stupid choice for talent points, it's just that it's not all that useful before a certain point in the game. Imp. Def. Stance really starts to shine once you get into SSC and The Eye, particularly when you first do Hydross, for absorbing some of the large amounts of magic damage coming at you in those and higher raids. Kara/Gruul/Mags don't really dish out enough magic damage to make it worthwhile, and 5 mans most definitely don't warrant the use of 3 talent points to take 6% off of spells that hit for sparse amounts, and 6% of them is smaller still. I can't name any point in time in those instances where I thought to myself "Man, 6% less spell damage would have MADE that fight," after a wipe. You're not stupid by any means, nor is the talent useless. It's just points that could be much better spent elsewhere before a certain point in the end game.
I took a loot at your armory and your talent build. The build looks good, aside from personal differences in taste, that being I've always hated Imp. Shield Bash and Imp. Revenge. Some people swear by them though, and they're not entirely horrible for 5 mans. I just hated having a mob stunned all the time. If you would like to move those 3 points in Imp. Defense, I would personally suggest either Imp. HS for improved rage dumps, or when the next patch goes though, Imp. Sunder. While Imp. Sunder isn't that great right now, because 3 less rage on sunders isn't game breaking by any means, once the -3 rage applies to Devastate as well it'll be an awesome talent. Just my personal comment, the advice can be taken or left however you like. :D