There are plenty of counter examples to your claim: YouTube, Google Maps, Picasa, various companies focused on voice recognition and Google Glass, etc...
Apple has bought several companies that had shipping products and just like Google, Apple didn’t cancel those. Examples are FileMaker, Logic, and Final Cut Pro. After it bought PowerSchools, Shake and Astarte, it kept their products on for many years. Furthermore, it is often said that Apple’s acquisition of NeXT was a reverse takeover.