We started doing video in multiple formats to reach all audiences. For non-flash video, you are limited to the video plug in the end user has. For most windows users, this will be Windows media player, Mac users, Quicktime. You can also do mpg for those that have players for mpg, or Real Audio format - but that is a very bad choice, as Real Audio has a reputation as a spyware app.
So now you're preparing at least two videos every time you add one. Each has to be encoded separately and uploaded, and you add links for an mpg download. Add to that, none of these formats "stream" well at all, most of the video has to load before it begins playing. You also have limited controls you can apply.
Another caveat, you can't get the <object> and <embed> tags to play nicely in all browsers. Basically you have to (illegally) place an embed tag inside an object tag to get it to work for both IE and FF.
I think you get my drift, stick with Flash. If you want a downloadable (why would you want to) encode an mpg and provide a link.
Your resizing requirement is going to be resolution-dependent, and may require multiple videos of various resolutions to be uploaded (lest your 320 X 240 video be sized to full screen and become pixelated.) I do believe Flash supports this as well, I remember seeing it in my travels through the help files.