While Ewan makes a number of valid points about the One AppStore, let me (as a commercial developer) raise some points in its defence, and tell you why I think it is a good idea.
1) Apple isn't the only party that sets restrictions on the kind of apps it allows in its store. Other resellers have very similar terms and conditions, the wordings in the contracts being so similar that they appear to be drafted by the same person doing a copy&paste from a master document.
2) In the Symbian world, the manufacturer can in certain circumstances also prevent apps from being installed on a device. Symbian Signed and Manufacturer-approved capabilities come to mind.
3) Discovery is as much of a problem on a PC with a browser as it is on an on-device client. This more a matter of having a good category system and lots of ways to sort.
4) As far as I can see, Apple doesn't look at the triviality of the app. It has a policy, but the app being trivial is allowed by that policy.
5) The problem with Apple (or any other party) having lost of control is because of the fact that these phones are subsidized; "He who pays the piper gets to name the tune". The number of people paying for the entire device themselves is too low to make an impact. Compare this for instance to the games console market, where hardware is sold at a loss, and costs are recovered by letting developers pay huge licensing costs for developing for a console.
Now for the good things on the AppStore, in order of commercial importance.
A) Developers make money. The single most important issue for a commercial developer. According to a number of public statements made by developers they are making lots more money than for other platforms.
B) Fulfillment costs are very low and known. This makes it possible to let the market determine the price of an app, and it makes a mass-market approach possible. With the high fulfillment costs which is is the norm for selling Symbian software (and also WinMob, Palm etc) a commercial developer can only cater for niche markets.
C) Obvious route-to-market. Having the AppStore frontend on the device itself and making it very easy to buy and install an app, these things make shopping for iPhone apps an enjoyable experience. There's almost no hassle, no endless are-you-sure dialogs or other things that might put off the punter. Again, a mass-market approach.
So I do too know which model I prefer. AppStore is not perfect, but it is much better than what we have in the Symbian world right now.