I did have to pay the $99 to sign up.
Apple has invested over a billion dollars in a data centre they are building. And they pay millions of dollars for hosting currently. the 30/70 ratio is fine if anything its the best in the industry and has been used for the basis of other stores like the Android Store the Nokia Ovi Store and the Microsoft Marketplace, although Microsoft also charge you after you release your 5th paid app or something like that.
Some of the costs involved:
1. The SDK for Developers had to be designed, tested and released with Support (Charge to development house: $99)
2. Every app you submit must be vetted by Apple employees (Unknown salary charges but lets say 30K per employee per year as a conservative estimate, we know they employ 100 people to do this currently. 100x30,000 = 3 Million Dollars a year and this is conservative)
3. Bandwidth costs of delivering each application, make no mistake Apple is delivering data in the Zettabyte range (ZB) Which does cost Apple a lot of money as they currently pay 3 different companies to provide them with the storage and bandwidth. That is why they are invested in that multi-billion dollar data centre which will be completed in a few years time.
Seriously though this deal is amazing. You basically pay them $99 USD for your entire company and can have as many employees you want develop apps. You are never charged for anything else. The 30/70 split is taken from each individual sale so you have no other costs to Apple. And in exchange they handle all your payment fees, marketting on their app store is free, they handle delivery, they also give you unlimited access to their infrastructure for out-of-app push notifications, update notification servers, in-app purchasing and many other add-ons that are priceless in this industry.
Theres currently 136,000 apps on the app store and the reason for that insane growth is the pricing scheme. If you had to pay a fee overtime you released an app it would die quickly. And lets not forget that Free apps get all of the above features just like the paid ones. And you'll find that on average an app on the store will get 10 to 20 software updates in its life time. Which means if you have a 10MB application (which is also quite average/usual for the smaller apps) you will be making a footprint of 200MB over the life of that app but you wont make any extra money (and neither will Apple). In-fact as time goes on and more and more apps arrive on the store it will become less and less profitable for Apple as they will have to spend more money delivering free software and free updates to paid software over time.
And yes 99 Dollars does get you a lot of hosting, but only for a shared host with 400 other websites. When talking about a dedicated box just for yourself that has to store TB's of data and make it accessible to millions of users per day the costs are incredibly high. That 99 Dollar price to be able to submit apps will get swallowed up pretty fast.