Having fought this battle at work for way too long, I can tell you that it mostly boils down to ideology.
Our product was originally a in house Java library that generated AJAX components. After it became unmaintainable (only 5 guys trying to create a product and maintain the library) I started looking into Flex. Flex did everything we were trying to do with AJAX and then some but there were those who fought me tooth and nail to go the HTML5 route.
They threw everything and the kitchen sink at me trying to dissuade management from going the Flex route. They would dig up ancient problems with the flash player, you name it. Steve Job's statements about Flash didn't help either. What won them over (or finally made them shut up) was the fact that there were no good HTML5 dev environments like there is for Flex.
What seemed to drive them was partially not percieving Flex as being open source and partially actionscript was new and unknown to them. Like the saying goes: If you have a hammer everything looks like a nail.
I hear you. Good work keeping Flex/AS as a development tool But. Have you ever looked at JS code to do graphical object manipulation. Its a bowl of bad spaghetti. And. Again. Steve Jobs should not have gone there with the blast that he did. All. His software visions were way ahead of its time for the hardware. So. I'm not buying that BS from him. Plus. Are all the browsers going to have a Vector graphics engine built in ??
It just sucks when a lot of developers get on the HTML5/JS bandwagon just becase Steve Jobs says so. Aren't there any NY'ers here on this forum ?