Your guess is absolutely correct. The main reason that the the sponsors pay for the teams is to get camera time. Sometimes when you see suicide breaks its for the same reason. The riders know they will likely get caught before the finish, but their sponsor gets a lot of face time when they are out in a break and for a team that doesn't have much in the way of superstars or stage winners it can be important - and hey you never know - sometimes they don't bother to chase you down or miscalculate chasing you down and you win.