I had this thought the other day as I was working on an army list.
What if Detachments and Formations were developed as a deliberate attempt to sabotage "net lists?"
After Games Workshop shut down their own tournament series, lots of armies were built the same way because the independent tourneys published the winning lists online for everyone to mimic.
The proliferation of Formations and all of the new codex specific Detachments could be the way Nottingham has decided to guide players into building lists that are a bit more fluffy and in character. Of course, the cynic in me says it could also just be a simple sales technique to sell more vehicles and models that are slow movers.
Either way, I love the bonuses of the Salamander Flame Strike formation, but I don't really want to take a devastator squad. At least the current rules don't force me to arm them with any actual heavy weapons...