I would expect that most people close multiple tabs with [cmd|ctrl]-w, precisely because of the back and forth mousing otherwise required. One thing I've worried about while using Chrome has been accidentally closing more than one tab at once, since, being a klutz, I don't have wonderful control over my index finger, and triple-clicking to select a paragraph is so common that I do it accidentally sometimes when intending to single click on a button or something. So far, I don't think it's actually happened very often, though.

  I would expect that most people close multiple tabs with [cmd|ctrl]-w

I find I use mouse close most often when I'm "info dumping", as mouse scroll and cmd+click to open a new tab are, for me, mouse operations. Rapid open/close of several pages is normal. Once I have 3-5 on a topic, I go "info diving" and nothing gets closed 'till the end, at which point cmd+w is how I tend to close out of the extra pages I had open. But cmd+w by even power users is, in my experience rare.

I like Chrome.

As it stands unless I'm wrong a user would have to go digging for these shortcuts online or by clicking help and actually knowing what they are looking for. Seems like a stretch for most browser users.