One exceptional run, at a moment of peak tapered performance, does not evidence of doping make. On one day, on a fast track, everything comes together. It's unusual, but it's not unheard of. not least because it was not, in fact, strictly exceptional -a wind assisted 9.68 the year before showed what was there.
Gay may have doped; anybody MAY have doped; but there is no evidence of it - he had a long, impressive career, progressing broadly as he oughta; his rep in the sport is as close to rock solid as you can get both in terms of humility and anti-doping credentials; he fits neither the temprement or physicality of doped ; he has voluntarily undertaken far more rigourous doping controls than most of his competitors, and hasn't, broadly speaking, tried to gain much PR out of it.
one has to be careful of simply suggesting ALL exceptional performances = doping - frankly, if you DO think that, why do you bother with any sport at all?