How Many Stars?

I keep seeing these posts about 4 stars...

I have 9 stars and still can't open up the end level (The yellow star is still lit - not grayed out) Does this mean there are 10 stars, and I need to be looking in the Wasteland for the final star?

Yes, you're right. There are 10 stars and the last one is in the Wasteland. I don't know exactly which star is missing, but maybe you've to look for a nearly secret way from one world to the Wasteland to find your star. A look at the worldmap is always helpful for questions like this.