Archie, you really didn't know the answer, before you asked that question? ;-)
It's common for someone to re-submit a coin, possibly to the same service, or to a different one, until it gets a better grading. That means they have it slabbed, and if it isn't what they thought, they break it out and try again.

Second point is, that besides not needing slabbing for casino chips, we don't need an extensive grading system either.

Third. These dang chips are taking over the house. Even the collections in binders and Dansco albums are too much. Image how much it takes for the chip in a slab?

Exception. Maybe slabbing for display purposes, with identification, but no grading would serve a purpose. Looks nice in the case... but not for marketing or evaluation.