Compared to previous versions of HTML, HTML5 makes it easier to create feature-rich Web-based applications that can be updated remotely with new functionality without requiring users to download and install an update each time.
Adobe is seeing increasing pricing of its rich Internet apps that are used by Web developers to create rich media web applications such as online games and interactive visualizations and are superior to typical HTML applications because they allow faster task completion, do not require opening up of multiple applications and are less-error prone.
Now that HTML (and Javascript and CSS) has finally evolved to the point where some basic rich media tasks can be accomplished (e.g. image slide shows), by all means.