Why do people always advise that we write 500 word articles or more? Does adsense have a problem with articles less than 500 words?

I'd believe it's harder to rank as it isn't much content but I just want to know that adsense won't ban for that.

I've read in several places that it's not about the number of words, but about content...

Even if you site was a collection of photo albums with no or very little text, that will be OK with Adsense as long as you're offering visitors stuff they're looking for.

it sure is about the content, not about the number of words, but if you write 100 words google would get less possibility to create keywords (where you site would be found) then whit 500 words.