There's actually at least two versions of Pure & Easy; an early version on the expanded version of Who's Next and a later version on OdRAB & SoRAB (and a few comps, like The Ultimate Collection). Both are good, but I think the Who's Next version has the edge.
I really think that leaving it off the album was one of Townshend's worst mistakes. Placing it near the beginning, and concluding with The Song Is Over would have made the album that much stronger.
I think a case could even be made for including songs like Too Much Of Anything. Something like:
1. Baba O'Reilly
2. Pure & Easy
3. I Don't Even Know Myself
4. Bargain
5. My Wife
6. Too Much Of Anything
7. Getting In Tune
8. Behind Blue Eyes
9. The Song Is Over
(And then release Won't Get Fooled Again b/w Going Mobile as a single)
I don't know how that would play, but you get the idea. Who's Next is one of those albums that's almost perfect as it is, but when you hear some of the outtakes, you begin to think it could have been even better.