You can bet your buttons that they give a lot more weight to the 'established' mod authors opinions than to the general community opinion. If someone like CJ or Sengir says they don't like a mod's balance, it won't make the cut. Guaranteed.
Wrong. They're friends and nothing more. CJ and Sengir hold no more weight over what goes into a pack than a friend of one of the modpack devs; which would seem to be very little. Both Eyamaz and Jaded are both very dedicated to creating stable themed packs that revolve around what they feel to be a balanced level for a majority of players or the balance that fits the theme of the pack.
Then again, that's generally why I consider the FTB builds a 'starting point' rather than the final game I am playing. I use FTB to find new and interesting mods (loved Horizons, new world, infamy, and magic farm for that very reason) because they often provide some mods I hadn't seen on the main mod list at the minecraft forums, and let me try them out without worrying too much about assembling a modpack around them. If they seem fun and workable, I check 'em for permissions and then migrate them to the server and the mod download.
As it should be. FTB is not meant to tell you how or what to play but give you easier access to mods and giving you, basically, new games with different themes. As well they will introduce you into the world of modded minecraft relatively smoothly.
Not too pleased with the most recent DW20 pack, though, it seems mostly more of the same. there are a few new goodies, like openblocks and waila, but for the most part it doesn't feel like it has changed much since 1.4.6.
I guess that works for maintaining server integrity, but it's kinda boring.
That's up to DW20. He is not on the FTB team and chooses the mods that fit his playstyle. These may not have changed much but they are still his preferred choices.