Microtransactions are the big income source for web games, income from ads tends to be fairly minor unless you can get millions of displays.
Most smaller games are made because someone wanted to make them, not because someone wanted to make money.

Microtransactions? What do you mean?

If you're saying you don't know what microtransactions are: It's a common source of money for game makers these days. I recommend you try Googling the term. http://lmgtfy.com/?q=microtransactions

If you're saying you don't know how microtransactions apply to "flash/HTML5 games," then that's a different question.

The second . I was unclear.

I don't see how this applies to flash games.

Check the games on kongregate or facebook, quite many of them use microtransactions to sell additional content, in game advantages, etc for flash games.

Aaaah, I know about that . Again, I should have been more specific. There are flash
games where they're hosted on a site that seem to get money only from advertising,
such as this.

http://www.flashtowerdefence.com/

Yes, some flash games only use ads, they don't make much money, the portal sites make money by hosting hundreds or even thousands of games (and some take 50% or more of the ad revenue from each game they host), in some cases the portal site is the only ones who get any money at all from the ads.