Let's see how it goes. If the sub model doesn't work they will probably try do deals for shorter periods or offer life time purchases. You can still offer those and do subs. People see $4.99/month and think oh that's a great deal and don't bother to add the cost up over so many months/years or a life time.Glad to see Apple finally putting some of their heavy pro apps on the iPad, but the subscription approach has me a bit worried, if a success, will they remove the charm of Apple Licensens on their desktop variants. Also, we already have lots of subscription both on business and the private front, so the market is quite saturated.
I though wish Apple would have provided both option, subscription for the ones wanting to try or use periodic times, and a "lifetime" like license as they currently have on the desktop app store, for the power users, willing to pay the price.
I just bought a piece of software the other day and it charges $4.95/month, $24.95/annual, or $39.95 for life time. Some people would happily sign up for the $4.95/month option and it'd cost them $59.4/annual. Or you'll get people buying annually. If they use it for 3 years then it'd cost $74.85. Life time is obviously the way to go unless you really can't afford a $39.95 one off payment