Just because a platform has a greater number of frameworks doesn't mean it is more powerful. You could even turn it around and say that the number of 3rd party frameworks being developed indicates the language is missing some important stuff and everybody is trying to solve it in their own way, with lots of redundant, very similar frameworks.
You are probably comparing your desktop/server experience wth those languages to a mobile platform. I program Java and .Net for server apps every day and iPhone by night. The two are a completely different world. In my dayjob I am using all the frameworks and libraries that make me more productive. For the iPhone I don't even go looking for them because everything I need is right there. (The only exception to that I could see is 2D/3D animtaion and games, for which there are several great frameworks for iPhone. But that is not something I Do.)
Fifty thousand apps in just over a year on a niche mobile platform can't be argued with. The Objective-C/Cocoa Touch platform is inmensly powerful.
Ask any mobile developer that has done Windows Mobile in .Net, Java ME or Android and see which platform they create their best looking, best function, most reliable apps on and which one is the fastest to develop for. Yes, that would be iPhone.
Maybe Mono Touch will bring that kind of quality and productivity using C# to the iPhone platform, but I am sceptical.
There is a reason why there is so much quality software for iPhone - and for the Mac platform for that matter - and that reason are the Apple SDKs and Objective-C.