not so valuable
Yes, MS or Apple might find a bug in an unreleased program if that bug has to do with overruns and security. If you are making a technical product it is unlikely that a new product would appear first in the app store.
Our last one went through nearly a year of beta testing at customers with different work loads. The MS and Apple testing is more in the realm of making sure the app does not hog resources, does not affect the OS, and does not affect other running apps. For example Microsoft Phone apps must come up within specific parameters and screens changes must happen within certain time limits. The hands on testing is more limited to metrics presumed to affect the oobe. Testing of functionality and fitness for purpose is entirely outside of their realm.
