Yes, well I read Jobs's letter. He should have had his secretary write it, since ancient technology he complained of was replaced some years ago by Adobe, I thought. (3D hardware code is yet to come; but will it be OpenGL or Microsoft's?)
Apple has always been fanatical about its interface, to the advantage of the user. However, there's a 'Microsoft' interface comprised of pop-up ads that just won't go away. Upon buying a SanDisk USB Flash Drive, I found 'U3' installed a Trojan and sold space for random pop-ups. Though I don't have Adobe's US$700 kit, my impression was that it's SDK did the same. Apple would never allow that; and it has always been Microsoft's worst security vulnerability. (Though FlashPlayer has many others, involving cameras, microphones, and large pockets (LSOs).
If this describes the FlashPlayer interface, anyone would know in advance that it would prove unacceptable to Apple. Apple's horror could, I suppose, be aggravated by its use (or not) of the GUI. The one point in Jobs's letter that was reasonable was Adobe's wedging its own SDK within Apple's free one: since MacOSX was released, no 2d-party application has given Mac users as much grief as FlashPlayer. I don't see an Adobe SDK helping.