But you also have to ask the following question: Would it have been more expensive to write it in Javascript in 2007 (with the same or close-to-the-same user ex

But you also have to ask the following question: Would it have been more expensive to write it in Javascript in 2007 (with the same or close-to-the-same user experience) than to write it in Flex in 2007 and rewrite it in Javascript now. My feeling (and I've spent some time thinking about this since we're going through the same thought-process right now for a project) is that the write it in 2007 in Flex and translate it now to JS is actually the cheaper option. The frameworks for large JS projects that we have now just didn't exist in 2007. This is without including things like comparing the present value vs. future value of money or the risk that the fancy Javascript code you are spending tons of time building (which was much faster to build in Flex in 2007) is going to be useless since no-one actually wants what you are building.