LAS VEGAS — Two top casino executives and the heads of several gambling machine makers agreed Wednesday that Internet gambling is inevitable and that U.S. companies and customers are vulnerable to overseas Internet poker operations.But the chief executives of Las Vegas-based MGM Resorts International and Las Vegas Sands Corp. differed during a keynote panel discussion with four other industry leaders at the Global Gaming Expo about whether states or the federal government are best able to provide oversight.Las Vegas Sands chief Michael Leven outlined doubts that he said company magnate Sheldon Adelson has about the profitability of online gaming if …