Compounding the error is the poor choice of middle-click as the alternative close mechanism. Many older mouses and most laptops don't have middle click. When browsing on my laptop I can't use the touchscreen to close a tab, as the hit area is much to small to accurately hit. Likewise, using the trackpad to land the pointer on the button is something I find difficult to do reliably.
I don't understand why the hit area can't be increased. There is little penalty for incorrectly closing a tab, as Chrome has a handy "Recently closed tabs" menu.
Edit: A search turned up the newer "Chrome Toolbox" plugin, which brings the missing double-click-to-close behaviour to Chrome tabs.