This is why I like uses direct quotes as much as possible. I'm not sure I can find any actual Shuttleworth commentary which goes as far as to say that users numbers are more important than contributor numbers. I've certainly not going to suggest Shuttleworth said anything like that unless I can find an actual quote.
However, It's reasonable to assume that usage numbers do matter to Canonical's business plan...even if the majority of those users are paying for support contracts. Just enough of them need to. So more users should bring up the odds of getting enough paying customers. I do have issues with the numbers Canonical quotes with regard to the Ubuntu userbase, because they haven't explained how they get that number.
It's also reasonable to assume that usage numbers do matter to the larger ecosystem. Contributors come from somewhere, they don't grow on trees. If Canonical is expanding the linux userbase with Ubuntu then they are most likely indirectly helping to grow open source contributors.
Even if Canonical employees are doing a particularly bad job of being good upstream citizens (Dustin Kirkland excluded for his upstream ecryptfs work, which should show up next time there's a review of the linux plumbing contributions) the more important question is this. Is the culture Canonical created inside the Ubuntu community helping to turn users into contributors at a faster rate than other distributions?
If you are a Ubuntu user are you more or less likely to be an upstream contributor than if you are a Fedora user or a Foresight user or a Mint user or a Gentoo user? Has Canonical really created a way for people to get involved in the larger open source ecosystem or have they found a way to get people contributing to a Canonical controlled walled-garden?
Translations.... how is Canonical fairing there? Have they made it easier or harder for Ubuntu's community translators to contribute upstream compared to users in other distributions? Translations should be an absolute slam dunk if Canonical really was building a better way to contribute to the ecosystem. And yet, Ubuntu translator contributions into upstream projects are frustrated by the process flow that Canonical has created for the Ubuntu translation community.