There are many factors that come into play. It depends on the website's purpose and ultimate goal.
I say go for it and write a blog about it.
I would like to sell some products. It very easy to put up photos, and videos in flex4. I just dont see why one cannot do that other than some kind of security issue, or the like.
Most sites today use both. You may find HTML easier for quickly showing a
layout of rich text and images. Flex will likely be easier for interaction
and create a better experience.