I suspect more to the point... if they release an SP4 then they would be locked into extending support by another 5 years.
They've already committed to making XP available via downgrade rights for another 10 years. I think a logical extension of that is the willingness to at least provide security updates and (paid) support for it. When large companies buy those droneware PCs,
they (and Microsoft) know they're not really buying Windows 7. They're buying Windows XP and getting a Windows 7 license along for the ride. They can reframe and "spin" the discussion anyway that they like for marketing purposes, but that's the fundamental
truth of the situation and we all know it. IT departments in most companies, particularly large ones, want to stay on the
trailing edge of technology for as long as they possibly can.
The motto of virtually every IT department head is this: if it ain't completely broken, don't even
think about fixing it. "Upgrade" is a four-letter word to them; say it only if you're looking to pick a fight.