Because it does not try to keep up with the fast-paced, complex flaws of Rich Internet Apps written by people who have no knowledge of information security and are only interested in getting attention for themselves and their shitty start-up.

Thereby rendering it unusable by people who want to create RIAs yet have deep knowledge of information security?

Hate to say it, but Firefox on OpenBSD is as vulnerable to this bug as any other browser. Of course, I doubt OpenBSD users have iTunes accounts...

I have an iTunes account.