By making these counter-offers Google is using real money to back up their assertion to (at least some of) their employees that their growth prospects are bette

By making these counter-offers Google is using real money to back up their assertion to (at least some of) their employees that their growth prospects are better than Facebook's. Think of this as a dividend-like unforgeable statement of corporate fiscal self-confidence. If enough Googlers go fishing for counter-offers at Facebook, Facebook will be wasting a lot of management energy reviewing and making offers to Googlers that were never going jump in the first place.