"Ubuntu Linux"

You have pretty much described why "linux" a weak brand and exactly why every single consumer oriented product is going to avoid using the word in its mainstream marketing materials. The dilution of its colloquial meaning to be equally and confusing applicable to the 1 billion+ different distributions on distrowatch means that from a product marketing perspective the meaning of "linux" is so that using it when describing your product to the target consumers is going to cause confusion. This is why consumer grade electronic appliances like network gear(NAS,print server, and routers) which use a linux based OS don't really mention it either.

Those of us who care about what products are shipping a linux derived OS ..those of us in the 0.01% tail of the technology consumer market...know how to find that information when we are looking to buy a NAS or router or phone or desktop or whatever (usually because we plan to hack it and extend its functionality) But, noone is going to build a viable consumer brand identity relying on the word "linux" as part of its core branding strategy, no one. There is nothing to gain in mainstream consumer purchasing culture by making it obvious that a particular product has a linux kernel in it. 99% of consumers frankly don't care.

-jef