At Buzzsprout we believe the number of subscribers your podcast has is not a good metric to track. Here's why...
Number of subscribers is a bit of a relic left over from the early days of blogging. Years ago FeedBurner was the killer app for anyone pushing content through an RSS feed. They did (and still do for some) a great job of providing bloggers with an approximate measure of the number of individuals currently subscribed to their feed.
In 2005 FeedBurner added support for podcasting. This gave podcasters an easy way to create an RSS feed and provided them with those same basic subscriber stats. Problem is those stats were designed for bloggers, not podcasters.
The number of podcast episode plays resulting from direct RSS links is diminishing steadily. The rise of the social web is allowing podcast episodes to be discovered and consumed in a variety of ways. Facebook, Twitter, website embedding, mobile, and direct linking to podcast websites are helping podcasts spread further then ever. None of these outlets utilize RSS and trying to measure reach based on feed requests results in a partial picture at best. More realistically what you’ll see is a terribly inaccurate and depressingly low subscriber number leading you to question your true calling as an Internet Podcast Celebrity.
Instead of subscribers, Buzzsprout tracks and reports on "Listeners." This sounds like subscribers, but it’s not. This is the number of plays we expect your next episode will get within it's first 90 days of life. Historical info is great but it get’s really exciting when you use it to predict the future.