This is another smart portfolio move from Google, though few companies could justify paying so much for the opportunity to monetize RSS feeds. In Google's case, the math is easy: Feedburner has around 700,000 feeds under management - that's a lot of ad impression and click opportunities. Plus, Google gets to integrate feed measurement into GA, automatic instrumentation into Blogger, and even, possibly, some integration with Google Reader, which is the #1 RSS reader in the market.
Measuring RSS usage remains a perennially tricky problem for blog (or other content site) owners. The Feedburner approach is to 'skin' the raw RSS feed from the real blog and re-present it with extra widgets (including tracking pixels and ads). When a user clicks on a link in the feed to view the original article online, this click is tracked through an adserver-style redirect, enabling Feedburner to offer the range of reports that it does.
The sharpest technical corner for a blog owner to negotiate in the process of setting up Feedburner is modifying the page meta tag information that tells a browser (such as IE7 or Firefox) what the address of the page's RSS feed is. Doing this is essential because if you don't (and the meta tag still points to the page's 'native' feed), RSS subscribers will just pull the native feed and not any of the Feedburner goodness.
But modifying RSS meta tags, whilst not terribly complex, requires some knowledge of HTML. There are still many blog owners for whom the phrase "requires some knowledge of HTML" represents a very, very deep chasm which they know they never have any hope of crossing in their lifetime. So a blogging platform that can auto-generate the meta tag for you is a boon.