There are a number of features dropped in 7, most notably the Removable Storage Manager. However, whilst there are a few features that are Vista only, I don't think most people would care about them - easier to run XP or 7 onwards. Can't think of any gaming reasons off the top of my head unless you count the removal of Texas Hold'em in 7.
Same reason there's little point to 95 - 98 did everything it did, but better. XP can run hardware EAX. 8.1 and below can run unpatched Securom/Safedisc games if KB3086255 isn't installed. Aren't there a few full screen graphics changes they made recently in 10? Anyway, the only essentials are probably DOS, XP, 8.1, 10 (for latest DirectX), and possibly 98 for a few old games that weren't as stable under NT.