Back in the old days, Blogger offer us feeds in ATOM format, and then they provided the popular RSS one :) Which gives us a way to do some tricks to offer both feeds, and let readers choose which one they wanted to grab.
But nowadays we burn feeds with FeedBurner, in order to grab some statistics of how many readers you have :) But still, some blogs, by default are offering the Blogger feeds default. So, in this case if you wanted to track how many readers you have by using FeedBurner, then maybe there's some number that has not been counted, those who subscribe to your default Blogger feed.
FeedBurner (after being acquired by Google) now surely are gettin' good ^^ They are offering the PRO versions. And now they have another good news for Blogger users, "FeedBurner Integration for Blogspot Blogs"
It simply redirect your feeds to FeedBurner one so that users will always grab the FeedBurner feeds (if you still don't have FeedBurner feeds, head on to the Quick Start for Blogger on how to make one).
By redirecting your feed, you can get a true picture of how many subscribers you have .... By redirecting your feed, you can consolidate any straggler subscribers and greatly improve your ability to effectively measure your audience.
So, how do you do this ? SIMPLE ! You just log into your Blogger account, select Settings | Site Feed, enter your FeedBurner feed address and click "Save Settings."
Voila. You'll be getting an actual number of your feed reader ;)