In a sense, wouldn't every invention be more of a discovery?

I can see where you're coming from. In my point of view, inventions are keys to discoveries, creating new ways to do what hasn't been done before, and to test the limits of possiblity. The invention of a spaceship can cause discoveries to be made of more efficient ships, not to mention discoveries of Outer Space. And yes, the invention of a mixed-media compatiable disc was the discovery of the other possibilites of CD's/DVD's. So, in a nutshell, inventions are just discoveries of how things work, but don't forget that the inventions wouldn't have been possible without past discoveries.