I believe that, but… why should that be the case? It’s a convention without a reference or motivation. I remember when they were new and I really had nothing to refer to and just having no idea whether they were on or off. The fact that I’ve got used to them now isn’t really that forgivable. In contrast, checkboxes not only have convention behind them, but mimicked filling in paper forms which many people were and are familiar with anyway. The idea that “filled” is on and “empty” is off seems inherently more intuitive even if you’ve never filled in a form if you just know that the concept of forms that you fill in exists.