On every windows widget I've encountered, you can right-click the selected text, and click copy. At no point must your mouse hand leave your mouse, leaving your other hand free to do whatever was so vital that it couldn't reach the keyboard.
The thinking behind the copy/paste metaphor is that there are many reasons to select text, only one of which is to copy it. You might want to, for instance, cut it from an editable widget, have your web browser treat it as a link, drag and drop it, etc. Select/paste is incompatible with this, as it is impossible to select text to further act upon it without clobbering the clipboard.
In my opinion, select to copy is unintuitive, not just different, as it doesn't conform to the underlying metaphor. The clipboard is (for better or for worse, and mostly thanks to apple) permanantly associated with the words 'cut', 'copy' and 'paste'. These hark back to the bad-old-days of assembling print articles by hand - you would literally cut, copy, and paste bits of paper, with scissors, photocopier and scissors, and glue respectively. Entrenched in users' minds is the concept of the clipboard - whatever you've cut or copied out goes in the clipboard, and the clipboard only holds one thing. For the clipboard to have got filled with something the user didn't cut or copy is unintuitive and confusing (Imagine if words jumped off the page just because you were looking at them...)
Intuitiveness aside, the 'market share' argument is a valid one. If linux is to expand its market share on the desktop, there are two sources of potential users - users poached from mac/windows, and users who have never used a computer before, and have no preconceptions. The latter group is getting smaller and smaller.
Select/paste goes against twenty years of convention in the desktop market (even dos used copy/paste), and the expectations of the vast majority of desktop users. Copy/paste is standard behaviour on both windows and mac, and therefore a de-facto standard, defiance of which will only serve to annoy potential converts.