Here is a direct comparison of wrestlingobserver.com versus WWE Network. Both are subscription services where you can hear or watch tons of audio or video "for free" with your sub, and can pick and choose what you want to listen to or watch. Several have mentioned this would be the best comparison, so here goes:
74% of our subscribers who listened to the post-Mania Wrestling Observer Radio audio last year also listened to the post-Mania Extreme Rules audio. Meaning if 1 million people order the Network for WrestleMania, using our site as a model that would mean approximately 740,000 Network subscribers would also likely watch Extreme Rules.
This, however, is not a fair comparison because we see about 7% growth in March/April for Mania every year and then a 7% drop when the show is over, because unlike the WWE Network people can sign up for only 1 month at a time if they want. Meaning there were people, I can't tell you how many, who were F4WOnline subscribers for the Mania audio but NOT the Extreme Rules audio. So the percentage of longer-term subscribers (a better comparison since you have to order 6 months to get WWE Network) who listened to both is almost certainly higher than 74%, perhaps even as high as 80%. So the idea that 1 million people will order a 6-month locked-in WWE Network subscription to watch WrestleMania, and then while their Network subscription is still in effect decide they WON'T watch Extreme Rules "for free" at any point is highly unlikely.
BTW, for those who wanted a WrestleMania vs. SummerSlam with Daniel Bryan comparison on this site, and again this percentage will be low because WrestleMania season is always the biggest of the year on this site in terms of numbers, it was 89%. And given the overall site subscriber base was probably 7% higher at Mania than at SummerSlam, that would mean VIRTUALLY EVERY SINGLE LONG-TERM SUBSCRIBER who listened to the Mania audio also listened to the SummerSlam audio.