Bolt's what, 22, it is entirely plausible that he just started to reach his physical peak, which could account for a large increase in speed from his early days when he was 18 and running in the low 10's.
He was pretty much this fast at the Olympics last year, he just started a smidge late and then pulled off the gas down the stretch. I believe they said had he not pulled off the gas he would have gone sub 9.6 last year, so it isn't like he is getting faster, he just actually ran the full race (and got a good start).