That is always true. You can test test and test some more. You do the best you can, but until it hits the public, it is not tested.The impression that I get from a LOT of companies these days is that the consumer are the beta testers.
I used to write business application software for a billion dollar company. You never know until it hits the road.
But your point is well taken; the better testing you do prior to release, the better your product will be.