HTML is a plugin
You have no idea how many times I’ve suggested using Flash for a website or part of a website to a manager or client and had them use the dreaded, “Flash? No, it requires a plugin so I don’t want to use it.” Here’s what wrong with that logic.

1. HTML is a browser plugin as well. Yeah, it is. It just happens to be hard coded into the browser which was a horrible idea. You see, a browser is an application whose main job is to communicate with your systems network. It also has added features like storing bookmarks, adding controls to move back and forth through your browsing history, things like that. But a browsers ability to render HTML comes from a parser/rendering engine.Now from the very beginning that parser/rendering engine was built into the browser application. That was a bad decision because it limited how a browser could be updated. HTML isn’t a static language. It’s gets updated from time to time. In the mid 90s when all this was brand new things were changing pretty fast. For instance when CSS came out you had to update your browser to use it. It may take a year or more for the browser to be updated. It would have been much better if you could have just updated your parser/renderer.
2. Okay, HTML was built into the browser but Flash was shipped with just about every one of those browsers. In fact if Flash wasn’t built into the download/installation of a browser people might think that it was broken.
3. Flash is more ubiquitous that HTML. It really is. Flash can run on a large number of mobile devices and that number is growing very fast. Can HTML run on your cell phone? Probably not but in 2 years you’ll have a hard time buying a cell phone that won’t run Flash.