They gain a 600ms advantage on the verification, then another few seconds on the download, depending on their bandwidth. 600 seconds average in a block, so if they manage to get an advantage of 10 seconds, that's 10/600 or 2% greater profitability than other miners. There will be less incentive for that when the reward halvings happen (fees double relative to subsidy). *shrug* Maybe they are also making some political point, or simply can't be bothered dealing with the txns. But the recent orphans should have cost them a bit. They are playing their own sort of game theories, and not always winning.