Druid is a special case where their primary stat is actually something meaningful to them. For Death Knights, Paladins, and Warriors, Strength is just something that comes on your gear, you don't go out of your way for it. The plate tanks will primarily go for secondary stats. They favor professions which allow them the flexibility to choose a secondary stat as the bonus. Blacksmithing for example is an excellent profession for them because gems (extra sockets) don't have to be a primary stat. Leatherworking for example would be relatively weak for a plate tank because even though the wrist enchants are nice it doesn't have the same flexibility as Blacksmithing's extra sockets where it litterally could be any stat.
Druids are different because unlike the other tanks where Strength is just something you have on gear, for a Druid Agility is also your most valuable tanking stat (in general). Because of this Druids can generally have a wider array of professions because almost all professions allow for a flat number increase to your primary stat. Leatherworking is good cause they get more Agility on their bracer enchant. Enchanting is good cause they get more Agility on their rings. Inscription is good cause they get more Agility on their shoulders. Blacksmithing is good cause they get more Agility gems. Jewelcrafting is good (until Blizzard makes it bad in the final tier) cause they get more Agility out of their gems. Alchemy is good cause the get more Agility out of flasks. Get the picture?
For a Druid...
Agility >>>>>> Everything Else
For a Plate Tank...
Strength <<<<<< Everything Else
And just about any profession can buff primary stats such as Agility, Strength and Intellect. Relatively few professions however can benefit secondary stats such as Mastery.
Blacksmithing, Jewelcrafting, and Alchemy are the three professions with the most flexibility. BS and JC you can change what you gem to get different results. Alchemy you can change what flasks/elixirs you use to get different results. While all professions are tuned to be relatively equal the fact that some can benefit secondary stats and some can't is a big deal to specs where your primary stat isn't king.
"In anything, if you want to go from just a beginner to a pro, you need a montage." /w TankSpot WTB Montage for Raiders.