As an advertiser myself, one can notice that most of the ads displayed are from NP members themselves!
Not only are they mostly very interesting sites, it also encourages visits in a different way (while financially contributing a little to support this community) instead of continually spamming the for sale advertising sections of the forum. The ads themselves are very unobtrusive (trust me, 99% of forums this size normally would capitalize on the traffic; clearly RJ has shown the complete opposite and is constantly trying to build new, clean, and novel advert programs that would better suit the needs of interested members). Most of the members on NP encourage the introduction of new ad display options, and RJ has been doing a great job in bringing it all together.
Not to mention, if you even bothered to look at the amazingly low rates offered on NP, you'd be astounded compared to ANY other forum of this size... so clearly you're 100% wrong about your assumptions here.