I've known 6 ESTP's... though one's a bit debatable as an ESFP (the female). And I've known about 5 ISTP's. Two of which are females.
In comparison, I know like a gazillion ENFP's.
I also know like a gazillion ISFP's, somehow.
But I do still think INFP, INFJ and ENFJ are less common. But this is just from what I've seen and known around me.
I honestly don't know how those statistics could ever be right, considering some areas have larger influxes of certain types than other areas, and then of course considering that not everyone has been typecasted.