I'm fairly certain Flash was initially intended as animation software, and is still often used as such. As long as the TV industry continues to use it, it's not going anywhere. There's a good many animated series that use it for this purpose. (Come on, I'm sure there's a few closet "Friendship is Magic" fans in here.)
The "real" purpose of flash is to provide people with an art/animation tool that saves in a vector format, rather than a rasterized format, resulting in cleaner images at any resolution, and tiny files that can be easily played over the 'net, even without broadband connections. Many of the current uses for it weren't really intended by the original development of the program, and came along later when Macromedia (and later Adobe) realized people had found other uses for it.
When people say HTML5 will replace it, they're usually thinking of the fancy webpage-creation aspect of it that developed later on. IMO, until there's some sort of WYSIWYG editor out there that reproduces the effect of working in flash for applications such as animation, I really doubt HTML5 will ever completely replace it. (Heck, that's why Silverlight hasn't done it.) And quite frankly, I want to be able to watch Strong Bad on my Trophy the way I used to be able to watch it on an Omnia 2.
And before anybody asks, I use Flash mainly as an art medium.