I watched it and the replay tonight. The replay picked up the race earlier, with the crash / slash chase down of the first breakaway, then the small move by Flecha and Ballan, then Chavenel, Terpstra, and another rider from Omega-Pharma-Quickstep along with Boonen chasing them down prior to the Terpstra-Boonen move.
I still say that Sherwin and Liggett are the best commentary combo in sport.
It looked like to me that Sky did not want to chase Boonen initially because they did not want to drag Ballan up to to Boonen. BMC had gassed itself earlier in the race.