Oh, well, it's true of most projectors, but it's possible that some projectors can actually do true 24fps but I've never seen one. I know that digital projectors in cinemas definitely have higher refresh rates then 24Hz, so it seems curious, that a home projector would do native 24fps.

But with a color wheel, the projector has to refresh 3 times for each full-color frame, so my guess would be, that its true refresh rate for 24fps sources is 72Hz, thus producing 24fps in full color and for higher frame-rate sources, it's capable of even higher refresh rates.