David, you cannot just put a blind eye to the fact that their code only works fror a particular version of an application. Something is definitely wrong there. If this were really the fault of Apple, then many more sites would be affected and not just the one created by the contracted developers. There's nothing wrong with investing money on an outside group of developers to do that job, but you have to make sure that what they create can scale properly. The Safari beta has been out for a long time now and those developers could have easily used that beta to test out the current development of said web application. They failed to do that, and now that the final version is out things are broken. This is hardly Apple's fault as the beta was made available to everyone for this sole purpose (consider why it's been made available even for Windows....how else would Windows developers be able to develope for the iPhone?).
No one is dismissing your complaint...it's just that it seems misdirected when it should be the contracted developers that need to check their code against all browsers that are available. This is why your company pays for their service. Personally, I just think that they are now trying to cover up their mess by passing the blame to Apple and convincing your company employees of the same.
Case in point: the school district I work for has purchased software from Excelsior called GradeBook that is used to input grades for all students in the district. AT the moment, this program requires Java in order to function. There was a time early on when only a particular version of Java was allowed....you could not upgrade to the newer version even though it might include security patches that the system might need or it would break the web app. I doubt that the district blamed Sun for this problem. Shortly thereafter, Excelsior made the code compatible for the newer versions of Java and made it so that there would be minimal breakage with subsequent updates. That to me is better development than blaming another company for your own mistakes and then charging the entity contracting you an exhorbitant amount of money to make the changes. Just my opinion, but you have to realize when you're being taken for a ride, especially considering the haste in which this web development contract was made according to your last post.