I went digging out of curiosity, and it seems you are correct. According to this article [1], around 80 of the top 100 airports have rapid transit connections.
[1] https://www.ptua.org.au/2015/10/29/busiest-airports-rail/
[1] https://www.ptua.org.au/2015/10/29/busiest-airports-rail/
And it's a bit stupid because the stations before and after the airport are the normal cheap price.