I agree with you on affiliate sales and some other intelligent things you mentioned. However, believing that all AdSense niches are profitable is lunatic. It's simply nonsense. I can simply post URLs here from folks who have great sites , tons of visitors and low earnings because they selected unprofitable AdSense niches. WW has tons of complaints like this one.
Go ahead place them in the thread and i'll be happy to contact them and show them how to turn their business around and fill my pockets with a bit of $ while I'm at it. The issue is not that they selected an unprofitable niche, the problemS are: 1) They are unaware what the high paying keywords are within their niche 2) Their content is probably of low editorial or authorative value 3) They are not aware how to optimize their content for maximum revenue (onpage/offpage optimization and other elements) 4) Someone has provided them with inaccurate information, too many $97 ebooks deals and pie in the sky BS deals on top keywords 5) They are not tracking or analysing potential hot spots in their niche by not looking/analysing their log files and adsense tracking info. AMEN!