The license incompatibility has kept it out of the mainline kernel for Linux, so it's not really a viable option there in many situations. Linux is definitely lacking in this department.
That's a minor concern and unrelated to the portability claim. That comes down to choice, and is not a technical consideration. I'm using it with Ubuntu 16.04 LTS and 16.10 where it works out of the box. It's most certainly portable to and from Linux and other systems; I've done it personally, and it works a treat.
Minor for some, major for others. And it is technical too, because there are maintenance ramifications for it not being in the mainline kernel, for example how quickly a security patch can be applied.
And for others a constriction on which distribution they can move to etc. It just reduces the number of situations where it can be used, even if you find yourself in one where it can.
