google search definitely has a moat. people build their websites to optimize for google's algorithm, therefore google users see better results -> google gets more users -> websites optimize for google -> repeat. Personally I never bother with 'bing SEO' or 'bing ppc ads'.
Maybe! Switching search engines is also very easy, and the top story on the front page is someone no longer using Google, but we know in practice almost nobody does that. As technologists we're much more likely to switch and know people who would switch.