I was discussing the current financial crisis with some friends recently, and we came up with a rather simple truth: The underlying problem of the crisis was too many people spending more money than they earned, living on credit and investment gains that only existed on paper. Thus now they'll have to save for a while, to pay back debt and accumulate a real financial cushion, before they can go and spend again. And when we were discussing guild policies on how to distribute raid loot, I suddenly realized that the same simple truth is also valid for that situation: If you give your main tank first choice of all loot, and equip him faster than everyone else, then at some point he'll have all the loot he can get with your guild at the current level, while the rest of the guild is still catching up. Just as in the long run you can't spend more money than you can earn, in the long run you can't always gain loot faster than your guild. At some point the main tank will have to wait for everyone to catch up, so the next raid dungeon becomes accessible.
That explains a lot of things. For example why it is usually the main tank who is at some point complaining that the guild isn't advancing fast enough: He got used to fast track gearing up, and is now unhappy with the inevitable wait for the others to catch up. It also explains why main tanks are quite often among those who hop from their current guild to the next higher guild: By simply exchanging your guild mates for a better equipped lot, you can get back onto the fast track again.
So for a guild to equip their main tank first is only a good idea if the guy is extremely patient and helpful, and doesn't mind to use his thus gained gear to help everyone else get equipped as well. If the main tank is highly ambitious on the other hand, giving him loot priority only prepares the next guild drama, where he either complains, or leaves, or both. Just like you can't escape basic economics and live beyond your means in the real world, a guild can't live beyond their means by equipping only a few people well, not in the long run. Albeit as Keynes said, in the long run we are all dead.