Perhaps a silly question, but what does the 12 in "web server extensions/12" mean?
It's the internal version number used by Microsoft. Although you think of it as Office 2007/SharePoint 2007, before the product was released MS folks thought of it as the Office 12 'wave' of products (SharePoint being in the Office family). So in SharePoint 2010 it's 14 (13 was missed because some people are superstitious about that number), although people are now avoiding using the 'hive' term in favour of 'SharePoint root'.
Using codenames like this gives MS the flexibility to change the final 'public' name based on e.g. marketing reasons. For instance, they sometimes get bad press for 'XXXX Product 2010' when the ship date slips into 2011 - which has happened in the past of course :)
Other groups in MS use other styles of codenames, the convention is typically to use places around Seattle. You might remember Longhorn (Windows Server 2008), Whidbey (Visual Studio 2005), Yukon (SQL 2008)...