There is almost 0 reason to go for expertise cap as a Warrior. It's nice to have for the threat boost but it's not necessary. As a full clear ToGC25 Warrior tank I've been running with about 49 expertise and 22 hit rating (and the only reason it's that high is because we haven't had access to 258 tier to swap out Chest/Helm until earlier tonight.) But back in Ulduar I wouldn't ever really gem for expertise unless under dodge cap which IS necessary. So long as you're over 26 you're good to go. No reason to gib yourself on avoidance or stamina for a little extra threat gen.
My armory if you're interested
The World of Warcraft Armory