> [...] lock down users machines heavily in the name of security
And because the browsers aren't the more recent versions with more recent bug fixes, it may actually increase vulnerabilities, making things LESS secure.
Not necessarily. I have a client that runs IE7 on all their machines, but those machines are completely locked down. We can't even run Webex on those things without IT coming down to install. Their own corporate website looks crappy on their own employee desktops, because the corporate anti-virus blocks one of the javascript's from running. (We had them whitelist it.) I challenge anyone to install any virus or malware on that thing.