I think what eHow does is take the value of the keywords you use into account, and the CTR on the AdSense Ads.
For instance, how-to's about Clickbank can make around 3-ish dollars a month from just 50-ish visitors, while a how-to about lock picking might need 5 times that many views in order to get the same amount of money.
The only thing that sucks is that most of the editors don't want people directly aiming at keywords, and they only want one article about the same thing.
Even though "How To Make Money Online using Affiliate Marketing" was available, and I wrote like the best article ever for it, they denied it (probably because its on eHow too many times) but also blacklisted the title so I can't re-submit another article with the same title (not sure if anyone else can either).
BTW: The only links you are allowed go in the "References" and "Resources" boxes. They are all NoFollow links meaning Google won't index them.
In conclusion: Writing for eHow is an extremely large waste of your time, and I'm surprised anyone writes for them at all. And it's too bad, because most articles would only need to be like 200 words.
HINT: There's a reason they named this section "Associated Content and Writing Articles"