This is not something hard to process. I can understand why apple would't want 3rd party applications on it because if the phone is bricked, the will cancel the account and they will lose money because part of Apple's income is from AT&T.
But then this confuses me:
I read this article from apple.com
"Developers can create Web 2.0 applications which look and behave just like the applications built into iPhone, and which can seamlessly access iPhone’s services, including making a phone call, sending an email and displaying a location in Google Maps. Third-party applications created using Web 2.0 standards can extend iPhone’s capabilities without compromising its reliability or security.
“Developers and users alike are going to be very surprised and pleased at how great these applications look and work on iPhone,” said Steve Jobs, Apple’s CEO. “Our innovative approach, using Web 2.0-based standards, lets developers create amazing new applications while keeping the iPhone secure and reliable.”
Web 2.0-based applications are being embraced by leading developers because they are far more interactive and responsive than traditional web applications, and can be easily distributed over the Internet and painlessly updated by simply changing the code on the developers’ own servers. The modern web standards also provide secure data access and transactions, like those used with Amazon.com or online banking."
It says something about 3rd party applications but I am not sure what Web 2.0 is if someone could clarify this.
As for people complaining about updating the firmware and bricking your iPhone, like Kash said, its there fault. It is not that hard, coming from a 15 year old I was able to revert from 1.1.1 to 1.0.2 on my own, install 3rd party applications and work flawlessly.
Due to this being one of my prized possessions I do much research before I do anything that would damage my phone in anyway.