I disagree about middle-click being a "poor" method. Middle-clicking is essential to mouse-based browsing these days, both for opening links in a new tab and for closing tabs. With middle-click, the whole issue of close button placement becomes moot.

Any laptop that doesn't have a separate middle-click button (hint: made by a fruit company laptops) likely provides some multi-touch method for middle-clicking. I also haven't come across a mouse in quite some time that does not have a middle-click (I use a including an 8 year old microsoft mouse).