Those two machines are special purpose boxes with migrated older XP licenses. One does streaming video output from Flash Media Encoder, which still seems to work a bit better in 32-bit XP right now. If the situation ever changes enough to justify such a change, I'll gladly move it up to a 64-bit W7 build.
The other is a dedicated JDownloader/Ventrilo/Skype/VoIP box (running an ancient P4) to allow communications and downloads to keep going while other machines are rebooting, under maintenance, or whatever.
That second machine could be migrated to W7, sure, or maybe even Linux, but I've got a perfectly servicable license for XP and the machine barely touches the internet outside of those specific apps.
Really, the risk ends up being pretty minimal after you factor in the firewall and very limited port forwarding.
Eventually they'll probably get migrated up, but I think the comm box will end up getting a total hardware change along with a new OS. That's a long ways away, though. No need to upgrade those two yet.