Do you all really think they put in a grease as good as or better than something like Mobil synthetic, or Mystik High Temp in those bearings?
LOL! You still not getting it, do you?
Truth to be told: properly manufactured/applied bearings with proper preloading, etc. can go a long way w/o the need of exotic grease. stock grease is designed to meet/exceed bearing manufacturer's designed/engineered specifics and never underestimate their ability to keep the bearings working.
Also something to note: unless you can pop the seals and wash out all the original grease packed in that bearing before pumping in some "exotic" grease of yours, otherwise, watchout for potential failures down the road due to grease incompatibility issues mixing original grease with wrong type of grease":http://www.bobistheoilguy.com/greasechart.htm
For more info, consult Kestas for he is a bearing engineer.