If you're willing to talk about number of subscribers you're revealing the rough revenue. You might as well just talk about revenue directly. People love to hear about someone making money, so it's much better link bait.
Thats the exact reason I didn't expect it to work. Looking at the product though, while the content you can get for free, the presentation is excellent. The digital is somewhat lacking though and frankly I find instapaper + kindle works just as well and is free.
"Hacker Monthly breaks $100k in revenue!"
The Balsamiq Effect.