No... that isnt true at all. I show interest by getting to know you. I want to know your likes, dislikes, goals, fears, etc. Thats how people show interest. You know how else females can show interest, its in the same way. 90 day rule for money and sex helps thin out those who arent going to wait that long with someone they are using. Im not gonna waste my time constantly paying for dates just to have sex with you after 3 months as girls arent going to waste their money to get a free meal after the 3 months.
I guess if you're dating multiple people, that works. In my experience what I have observed, men that date one woman at a time, wouldn't let her pay. So, yeah if you're a serial dater this could be a good technique to weed some people out.