Of course they are paid for including the toolbars in the download. Its how the free downloads are paid for.....without the addons, there wouldn't be anything free. Its simple enough just to untick the box at download time.
And don't let the addons put you off Avast. The new version is quite brilliant, with an advert blocking web plugin, and a routine which checks how up to date other software is, and whether its vulnerable. It will check and recommend updates for flash / adobe / java and more