There is much less emphasis on compression skills. It's more important to recognize bulky objects and simplify them, than it is to juggle all the variables in typical digital video compression. Some things are easier in video than Flash Video can require less processing power. Digital video presentations tend to have a narrower range of processor loads than the range of various Flash presentations. In Flash, If many elements are animating at once, if partial transparency is applied to all of them, if they are changing shape, if they cover a large area of the screen, and if MP3 audio is decompressing in the background while a download is simultaneously occurring, then slower processors can definitely show the effects of all these requests.
Video can deliver a more predictable frame rate.
Video codecs are time-based animation streams, and most movies will drop frames if necessary in order to maintain the desired frame rate. In event-based animation systems, such as Flash and Director, each frame is usually guaranteed to display, and time will be dropped in order to ensure that each frame is seen. Audio synch is usually simpler in digital video. Video can usually offer greater detail at lower cost. Some codecs will display a single bitmap more economically than JPEG, and many codecs can use interframe compression to make a bitmap stream more compressed than it would be as individual images.