As far as I understand, this is the correct answer to the OP. Why do companies with a large IT infrastructure willing to pay extra to get IE8 support? Because their IT infrastructure has standardized on stock Windows 7 (which comes with IE8, and not IE9 like another poster here claimed), and until they move away from that platform (sometime in late 2017), IE8 is the standard supported browser.
I've been in such a company (I wont name names, but its a leading computer technology provider, possibly the leading provider) which works exactly like that. Recent engineering systems come pre-installed with Windows 8 and now 10, but anything else is running Windows 7 with a stock configuration.