My interpretation of the article differs. The way I read it, the 451 group are only claiming that suing TomTom for their use of the kernel is very different from suing the open source community in general (however you would go about that).
I strongly suspect that the 451 group have not actually checked how much TomTom is customising the Linux kernel.
As to their conclusion, it seems unforgivably naive. If the lawsuit goes Microsofts way, we can be reasonably sure that they will go after more companies, and Canonical Red Hat and IBM won't be far away.