In order to host a product, in this case manga and anime, the site needs to have copyright papers/documents from the owner. Viz Media holds such rights from TV Tokyo and Jump Comics. There are other sites such as Crunchyroll that are official ones but in these sites you have to pay certain charges in order to watch anime or read manga. Generally, the official sites offer anime and manga only when you pay certain amount of charges.
I am not complaining. I love this site. However the sales of DVDs and Manga volumes decreases drastically because of sites like NB that hosts anime and manga for free. What is more you can download high quality and save it to a hard disk. That is why people won't bother to buy DVDs and manga volumes when they are released in the market. A great loss for the producers and mangaka. SO I don't call it advertising.
P.S I have this feeling that the thread will be closed pretty soon since we talk about negative aspects of NB. :p So let me say something before it will be closed. It is because of sites like NB, people like me get chance to enjoy such a great anime and manga. The DVDs and manga volumes are barely available in my country. If you order in online then the cost will be like four times and will not be affordable. Those DVDs that are available in shops are affordable but like I said they are very rare. And most of the time, they do not offer new releases.
I am really glad that there are sites like NB out here.
At OT: Windows 8 does have some cool applications. i am enjoying them right now. :D