It's not just about openness, it's about the upstream contributions too.

As a case in point, the Linux Foundation released a report in April 2013 about the contributions that make up the Linux 3.2 release. There's a couple of tables in it which show which players sponsored how many changes. The one below is the changes since 2.6.36. notice where Nokia are and where Google (who benefit most through Android, and their own infrastructure uses company wide) and also AMD who make shitloads of hardware. BTW this is Nokia who canned their Linux phone involvement last year, and the team that made the majority of these contributions have popped up elsewhere and are still working with the community and pushing future contributions with them too.


edit: btw, Canonical doesn't pop up at all in the report. The link Mikecomputing shared from Phoronix makes the argument why using CLAs with a GPLv3 licence is A Bad Thing.