Yeah, I'm not really sure I believe this stat either - it seems way too low but I could believe maybe its closer to 50%.There may be some fact to that but my wife can cum with just penetration in either her pussy or ass, she's not the only one I've come across like that either, I had an old girlfriend that was the same and I've been with other women that were able to cum from just penetration, I'm no one special so I'm sure other men have come across these women, saying these type of women are rare is definitely wrong.
I feel like in a lot of cases it is probably inability of their partner or the women's lack of knowledge of their own body. The only woman I ever fucked multiple times who couldn't orgasm from intercourse was a 21yo who had never had an orgasm at all before and I figured, if she can't make herself cum, how could I? I probably would have enjoyed the challenge of trying but we only dated a couple months.
One issue though is I've read it takes women an average of 15m to become fully aroused and able to climax, whereas it is way lower for most men.
I'd like to think I'm skilled at sex but, in reality, probably the #1 reason I've made most of the women I've been with cum is just that it takes me a long time to cum.