Actually, I think Rob is extremely lucky to be cast on the Ometepe tribe. I believe if he'd been on the Zapatera tribe, those guys would have plotted like crazy to get rid of him right at the beginning, and they probably would. (Look at how they went to extreme measures to get rid of Russell.) Then again, I can't discount the fact that Rob being more likable might have been able to secure a solid alliance on Zapatera anyway. But as I look at the personalities of both tribes now, I feel that Rob could be in trouble had he been on Zapatera.
Of course, I still give due respect to Rob's gameplay. But if not for his tribe members being so willing to eat out of his hands, no gameplay would keep him in too. So... Let's call in luck + strategy.