But it's not--it's proprietary to Adobe and was designed for the desktop and not mobile. And while performance on Windows was always pretty good, it was horrible on Mac OS X. Flash is the single biggest cause of browser crashes on the Mac.
Ironically, Apple choosing to support HTML5 video and encouraging their developers to do them same got them lots of criticism.
And even if your browser didn't crash, your machine would slow to a crawl because almost all of your CPU cycles got hijacked by Flash, even on new hardware. Apps like ClickToFlash (http://clicktoflash.com/) were required to make surfing the web tolerable on the Mac.
Eventually Apple stopped including Flash preinstalled on Macs; many Mac users removed Flash so their machines would run cooler and faster and with more stability. And existing users realized (thanks for articles like Going Flash-Free on Mac OS X, and How to Cheat When You Need It (http://daringfireball.net/2010/11/flash_free_and_cheating_wi... they could uninstall Flash and the world wouldn't end.
Even when pundits were producing FUD constantly about the lack of Flash on iOS, even predicting that Apple would eventually relent, I knew it would never happen.
Apple would never allow something they didn't control to become the video or animation standard on their platform. And certainly not something that would have a detrimental impact on battery life and wasn't designed with touch in mind.
Apple didn't just win today; they won when they said publicly what many of us already knew: Flash is legacy technology that's not necessary going forward. Which they've proven repeatedly.
On my Mid-2009 15-inch MacBook Pro running Mac OS X 10.7.1 and Safari 5.1, I get 180–190 frames per second at 1000 particles using canvas.
On Chrome, using its embedded Flash player on the same machine at 1000 particles, I get 30-40 frames per second--big difference.
Like all of major browsers, most graphics on Safari 5.x are hardware accelerated via the GPU.
To sum things up: Flash is significantly slower than HTML5's canvas running the same benchmarks on current browsers.