slowly lowers flamethrower indeed, you're right, HTML and WebGL with JavaScript or webasm can do anything flash can..
They can't do it in the cycle-count that flash could (I remember seeing 3D vector demos running in 640x480 pixels on my 133 mhz pentium), but they will do it, and probably look almost identical across two different versions of the same brand of browser..
But the real point is the authoring tools, and there simply aren't any.. We're stuck in the early 80s with a f*cking text-editor for GUI work..
Geez, there were authoring tools for making nice GUI applications in the Windows 3.11 era.. But modern web development has yet to reach that level of maturity.