He raises some good points - concerns that I share.
We *reluctantly* looked into Flex a few months ago. We did this after trying numerous Ajax frameworks. We were not interested in a widget here or there that did some Ajax booya. We wanted to build a full blown RIA app for a very complicated system.
After suffering through severe pain in trying to get Ajax frameworks (choose any one you like) to work with Firefox, IE 5, 6, and 7 we threw our hands up.
We heard good things about Flex so we tried it.
We weighed the pros and cons of its openness (at the time it was just shared source equiv.) and decided to proceed further. Since then, they have opened up Flex - or stated the intent to under the MPL license. We were very happy to see this development.
Flash - is of course still proprietary. Mark is focused on this. He raises good points - concerns I share in a style try not to.
Adobe is showing a good direction towards opening things up further. I'm hopeful that some day Flash will be open.
In the meantime, our business has competition and we seek to beat it with the best systems we can build. We weigh the pros and cons, make our choices, and live with the consequences. Just like Google Finance and YouTube (properties owned by Mark's employer that both use Flash) do.