Keyword Research using 100k Adsense

Hi,

I've git a question regarding the keyword research technique outlined in 100k Adsense Blueprint. The author mentions to use spyfu and check how many advertisers are active for a specific keyword. He also states that there should be at least 3 advertisers.
My question is if and why it's that important to check that even though there are other high paying niches without any advertiser (n/a).

Checking out how many ads are on a search is a good gauge of how profitable a keyword will be. Most keywords that have ads on them have searchers that are willing to spend money, otherwise advertisers wouldn't bother spending money to advertise on them.

Because finding out if advertisers are willing to fight it out for the top spots gives real time indication on whether your clicks will earn more $. More advertisers >> more hula mula.

Always look for "exact" for high adwords competition and if possible EMD

In my opinion, there is no niches in which offer a lot of money for per click and no advertisers a long time. There is or low traffic on these words, or something else is wrong. Does Spayfu show such data?