I would suggest you spell that out more when mentioning this topic as "support" on its own has some ambiguity. Reading that line basically put our plans for upgrading our 2.3 setup to 2.5 rather than 2.4 over the summer on hold. Some other people might not have sought clarification and just decided to stick with what they've got on that basis.
Which is a problem that Google Apps don't really have. If they upgrade and break something on IE8 then your choice is like it or lump it. Everyone running their own Moodle has to take that upgrade decision independently, so you might want to put the emphasis on the carrot (e.g. the drag'n'drop functionality has been really good for getting people onto Chrome/Firefox
at our institution) rather than the stick.
You might also want to be explicit, in the dev docs, about exactly which versions of IE
you are happy to actively and intentionally break. I had a conversation in a bug report in the last couple of weeks that suggested that "supporting" IE7 was still a requirement for any change, and your comment here similarly focuses on "new bugs" rather than on development decisions that will knowingly exclude IE8 from working for large swathes of Moodle e.g. adopting JQuery 2.0 (I realise that Moodle doesn't use JQuery, but it's the most prominent 3rd party library example I could think of that has dropped IE8 support and provides a benefit, they claim it's faster, as a result) so you might end up in a worst of both worlds situation where you're actually doing the work (or holding back progress) in order to support IE7/8, while also scaring off people from upgrading by announcing you don't support them.
Finally, will there be any kind of popup or notification for users of old browsers built into Moodle? I'd quite like it if there was an admin settings that let you tick off browsers and actively exclude anyone using say IE6 or IE7 and present them with a page of information and links to upgrade, whereas say users on IE8 or Firefox 3.5 just got a nag screen and were allowed to continue. We'll probably end up doing something internal anyway, particularly as we want to be a bit harsher with people coming from within our own institution, rather than someone forced to use old IE in a developing nation or government department but if the idea is to use Moodle to actually shepherd people forward then something built into the platform would be good.