Originally Posted by
Avadon
Anyone who is serious about end-game tanking with their DK is going to take avoidance over expertise, for reasons that have already been pointed out. Personally I rolled a NE for my prot war because of the 1% dodge (1% avoidance) and now they're changing 1% dodge to 2% chance to be missed (twice as good). 3 expertise is nice, but not all that hard to get with gear. 2% avoidance as a tank, for free... invaluable. Remember avoidance has exponential returns, and Death Knights being avoidance tanks to the extreme, that 2% will go even further on a DK than a prot war (though some will argue that chance to be missed scales inversely with dodge/parry).
If you're still not convinced, consider talents in the frost tree: 2 talent points gives you 2% chance to be missed (NE racial is worth exactly 2 talent points); how many talent points would you spend to get 3 expertise? 2 talent points in frost gives you not only 4 expertise instead of only 3, but also +4% damage done to victims of frost fever. Granted the 4 expertise with damage boost is much deeper in the frost tree, but it somewhat goes to show the value of avoidance. Also in the blood tree there's a talent that's +1% Str, +1% Stam, +1 expertise per talent, right? Few people would take a talent that just gave 1 expertise per talent point (tanks I mean, unless parry-shred is a huge concern on some of the new content); everyone takes 1% avoidance per talent point. People have considered some of the +Str% talents to try to buff their parry rating for avoidance. It isn't worth it, but consider that the NE racial (not considering inverse scaling) would be like having 98 parry rating for free, from an avoidance stand-point.
Another thing to consider is that while expertise is still very important for DK's, you'll hopefully be going frost, which gets 10 from talents anyway, and will also be using a fair amount of spells for agro, which expertise won't help anyway. Also with the change to rune strike, getting dodged or parried isn't nearly as hurtful to your TPS as it used to be, and tanks don't have as hard of a time holding threat anyway, so the real focus should be on taking as little damage as possible anyway since threat generation is almost a non-issue.