I know they're not needed if you aren't using the | or in there... but with the OR you'd think it was safer. I'd check the MSDN pages regarding CC's to be sure. It's possible they are necessary when using | and it just looks like it's working because the !IE thing makes no sense... only IE would read the "not IE" comment, so no not-IE browsers will see that.
<!--[if gte IE 8]> stuff for browsers IE8 and IE9... IE10 does not do CCs<!-->
I would think the parens would work like this anyway:
<!--[if (gte IE 8 | IE 6)]> stuff for browsers IE8 and IE9... and IE6 (so, skipping IE7)<!-->