You still can't install any application on the device. You could easily argue a lot of things but what on earth are you talking about, as far as the initial success of the iPhone is concerned?
You're confusing the use of the word "any" here. In the previous post, it was used to mean that there were _no_ applications available for the iPhone.
You're using it here to mean "you can't install arbitrary applications" which is something different.
As far as the initial success of the iPhone is concerned, the device gaining traction without "any" applications (in the first sense) is largely important when speaking of the necessity of the App Store.
