Wow, lots of meat there to discuss. I'll be brief as I'm running out of time.
1.) All four tank classes are more or less equivalent in abilities for tanking. Each class has its own strengths and nuances, and obviously spec and gear selection matter as does player skill. Paladins are strong tanks, as are DK's if that helps a couple questions there.
2.) DK's are good raid buffers, they have some buffs in common with Shamans but that's where lumping in the same category ends. Blood offers the +10% AP buff that Enhancement offers, Frost has the 20% melee haste mirroring Windfury totem, and Unholy has a +13% spell damage buff to match Balance Druid's Earth and Moon, and Afflic Locks' Imp Curse of Elements. All DKs offer Horn of Winter which is a shout-esque equivalent of Strength of Earth totem. DKs do strong damage and tank very well. Shamans have many great totems, Heroism/Bloodlust, and spec-specific raod niffs are all great to have. I'm not sure what else you're looking to get from articles.
Welcome to the new world order, I like to think it's a lot smarter than it used to be.