Yeah I was at that game-it was v Luton at Kenilworth Rd and I was also mad when he "refused to play" for us. That wasn't the case as I found out from the great man himself (he lived opposite me for years until fairly recently) that Villa as part of the deal didn't want him cup tied which obviously would have been if he had played.
I have no idea whether Richardson refused to let Dublin play in the Luton game or not, but if he did so he didn't bother to tell Strachan, as he was furious with Dublin. What is fact however, is that Dublin was already cup tied having played (and scored) in the previous round, so if he told Adge that was the reason Richardson wouldn't let him play, that was plainly untrue.