It's not about which companies is contributing..the most.
It's about which companies are contributing "enough." Is Canonical contributing enough? When Shuttleworth talks about Canonical's business needs, and how Canonical needs to see upstream projects change how they are doing things to better serve those business needs... is Canonical contributing "enough" to those upstream projects to have their business needs seriously considered? Shuttleworth has been very public about challenging core upstream projects like the kernel and X.org to do things differently for Canonical's benefit. It's only fair that Canonical be challenged to pony up the manpower to make that happen.
A significant amount of the heat being generated now is in direct response to public statements Shuttleworth has made. Which other company in that list of companies has a CEO which likes to publicly blog about how he feels upstream projects should be doing things?
If you just stick with actual corporate entities who are paying developers to do open development... is Canonical doing their fair share to re-invest in the open source infrastructure that everyone is using?
Right now, at this very moment in time...
If you are a skilled open source developer, with intimate knowledge of one of the critical subsystems that make up a linux desktop, looking to get a pay check for your work, is Canonical's commitment to supporting the ecosystem strong enough for you compared to other potential employers looking to hire you?
I'll let you in on a little secret. The pacing item in the continued advancement of the open ecosystem are upstream developer manhours.... not downstream integrator manhours...nor even users. The real work and challenges are in front of the upstream projects themselves. As downstream integrators, we should work on increasing the available upstream development manhours, or else we we'll run out of new things to integrate.