FYI, it's generally accepted there are five different categories of trademark, each more defensible than the next. The least most defensible mark is a "descriptive" mark. Like "facial tissue." Had the Kleenex brand chosen "Facial Tissue[tm]" for their mark, they may well have lost control of the mark because generic terms cannot function as trademarks.
We all call them Kleenex, but they are facial tissues. If someone had tried to trademark 'facial tissue' we would be in the same ballpark here.
The most defensible mark is a fanciful one, that is a word which does not otherwise exist (Kodak, Xerox, Pepsi, etc). Afaik, Kleenex actually is the best possible name one could choose to associate with tissues, since it is entirely fanciful (and Kleenex company has done a good job associating their name with tissues). As an aside, it is possible for a diluted mark to lose its protected status (such as with Bayer's "Aspirin" analgesic).
These marketing people might as well start trying to trademark things like 'desk' 'pen' or 'screen'.
Netbook would probably fall under the "Suggestive" trademark category (the third most defensible category, behind Arbitrary and Fanciful). Net and Book both exist as words, but were previously not widely applied to this sort of device.
So, in conclusion, "Netbook" is nothing like "pen" or "desk," as far as trademarks go. Neither of these examples would even be registerable, unless they were referring to something they weren't (you could make a ketchup product called "DESK" or a cell phone called "PEN").