In placing the close button on the right, Google have assumed that in the majority of cases, users are going to be wanting to close the most recently opened tab

In placing the close button on the right, Google have assumed that in the majority of cases, users are going to be wanting to close the most recently opened tabs first (likely to be the ones to the far right of the tab group) and have accordingly placed the close button on the right. Why? Because not only does this give the user the ability to close a number of tabs in one go without moving the mouse pointer (which Safari does not), it also means that the app does not need to exhibit the ever-so-slightly less normal behaviour of the ‘delayed resizing’ in the most-common case. I would also wager that while Chrome is available on other operating systems, it's probably catering to Windows users by keeping the close buttons (be it a Window or Tab) on the right where most user expect them to be. Similarly, Safari, more at home on OSX than any other OS, would cater to those users by keeping it on the left. As for the slick behavior Chrome emits when working with Tabs, I'll admit I never noticed it. But maybe that just proves the author's point, "It just works!"