It seems sort of unfair to compare kernel contributions from Canonical to a company like Red Hat simply because of the time-frame during Linux's development that Red Hat was a part of. Isn't is possible that Red Hat helped out more because it was around closer to the start of the Linux project?
Also, Canonical's and Ubuntu's strengths may not lay in kernel development, but instead pushing the boundaries in what can be done on the UI. I certainly don't remember Red Hat or SUSE doing the sort of risky things with their UI that Canonical is willing to try.
This is actually what the conclusion of the article says - that Canonical is taking worthwhile UI risks, and probably doesn't feel much need to work on the kernel.
Also, Canonical's and Ubuntu's strengths may not lay in kernel development, but instead pushing the boundaries in what can be done on the UI. I certainly don't remember Red Hat or SUSE doing the sort of risky things with their UI that Canonical is willing to try.