Learning another language is an overhead, an investment you make that increses your skills and broadens your abilities. If you want to write applications for iPhone OS and take advantage of the huge market that Apple has created, then learning Objective-C and Apple's IDE is an investment in time that you need to make. It's just what you need to do. Many developers from other backgrounds have already started programming for iPhone OS and met with great success. If you're experienced in object oriented program design, or C++, then the transition isn't that difficult.
As a long time Mac user, I've experienced a lot of Mac applications that have been straight ports from other platforms and they are, for the most part, pretty awful. I can understand from this why Apple wants its developers to code iApps natively.
This 'lock in' makes perfect sense for Apple in other ways too, ways in which end users and developers will benefit. Imagine that Apple allow apps to be ported from Flash. Developers would stop coding natively for iPhone OS as they would be able to create their apps in Flash and distribute them as web apps at the same time, reaching a greater audience. Then add in Android, Blackberry & other export options for Flash. Soon enough Flash would be the only IDE in use and platforms such as iPhone OS would be at the mercy of Adobe. If Apple were to introduce new features and efficiencies to their hardware and APIs, they would have to wait for Adobe to implement them in its Flash translation layer before the features would really become available to end users. Even the most willing and motivated of developers would not be able to get around that, they would have to wait for Adobe. So in the end, Apple would lose sales and credibility, and good developers would get screwed because they wouldn't be able to out pace their competitors in updating their apps to take advantage of new features. Everyone becomes 'locked in' to Adobe. Given Adobe's poor history when it comes to timely bug fixes and support of its OS X applications, I do not think that this 'lock in' would be a nice place to find yourself, whether you're Apple, a developer or an end user.
If you don't like Apple's stance then develop for other platforms and buy other products. But if you want to be in on the action, then accept the rules as they are not unreasonable and will ultimately benefit everyone.