Definition:
A site is made for AdSense if its sole purpose is to get users to click on AdSense ads.
A site is NOT made for AdSense if its primary purpose is to provide unique content and you decide display ads as means of generating revenues, utilizing Google AdSense, YPN and other contextual advertising networks.

Why are everyone buying MFA sites?
The thing with MFA sites is that they work. Most people don't understand Google AdSense and don't realize clicking on a site filled with nothing but ads generates money to the site owner as well as Google, costing money to an innocent advertiser.

Revenues from MFA sites typically average well below $100 per day, however smart marketers put together a thousand of MFA sites, accumulating a sizable revenue all sites combined.

The Problem:
MFA sites are a violation of Google's terms of service. Google is working hard on bringing down all MFA sites, as part of their fight against click-fraud. If identified as an MFA site, your Google AdSense account will be shutdown and any revenues accumulated to date will be lost.

Alternative Solution:
Instead of creating an MFA site which is 100% ads with no real content, create a network of small sites, each revolving around a particular niche, each with a few quality original articles in that particular niche and utilize Google AdSense to integrate ads as part of your articles. This way you are not violating Google's terms of service, you are providing quality original content to your website visitors and if done right, such a network of sites can generate a sustaining revenue from contextual advertising over a long period of time.

See screenshot showing a sample GOOD way of integrating Google AdSense into a bare-bones 5 articles content website. Users are bound to click on the ads as they appear to be relevant and flow well with the rest of the site:

It is very good article.