Please don't say hit and expertise aren't important for tanks. Just don't.
Here's how all these stats work. Hit rating increases your chance to hit with your melee swings and melee based abilities (such as Crusader Strike)and also your spells but this is not important because as far as i remember you get increased hit rating on spells for paladins, this stat is very important to cap because it's the most reliable thing to increase your threat or TPS (threat per second). Expertise rating increases your chance for your melee attacks to not be dodged or parried, this stat has a double edge effect: while it still increases your TPS output reducing the boss' chance to dodge or parry your attacks, it also increases your avoidance slightly. You're gonna wonder how, well there's an in-game mechanic which acts this way: After you parry an attack your melee swing resets, to be more understandable after you parry an attack you immediately strike with a melee swing thus ignoring your attack speed. Why is this an avoidance increase? Because any tank has a standard hit table: this is filled by 9% chance to be missed (as far as i remember, i might be mistaking), the value of your dodge chance and the value of your parry chance, and then the value of your block chance.
Let's say you have 11% dodge 10% parry and 30% block, your hit table will look like this: 1-9 missed, 10-20 dodge, 21-30 parry, 31-60 block. This hit table provides the game mechanics enough information for it to calculate each boss' attack. So in a normal (expertise capped) fight, your boss attacks will only hit you for the full value 40% of the time. If you're not expertise capped the boss will hit faster, and all the avoidance stats will diminish in effect thus lowering your avoidance and being hit more.
Now the problem is it's pretty much impossible at this time to reach the hard cap for the expertise rating and not loosing alot of important stats (if not impossible at all), so that's why hit and expertise caping are considered a waste. I myself use full hit cap (provided by food and reforging), and soft expertise cap (only caping dodge rating, also through geming and reforging). I choose specing like this to provide more damage output and more TPS output.
If your guy just stated he needs expertise to increase his dodge he's wrong, if he knows what i just wrote here then he's right. Either way caping hit and expertise is pretty good especially if you have a good dps group in your raid.