Same experience on all platforms
As much of a patch palooza Flash is, it still is the only web technology that provides the same experience across all platforms. HTML5 does not do that! HTML5 isn't even rendered the same using various browsers on the same OS. Even the same browser on different OS renders HTML5 differently. And there is not a single browser available that fully supports all of the HTML5 specification.
Killing Flash may solve one or two problems, but it removes the only option to deliver the same UX to users regardless of OS/browser used. All the Flash bashers should now fix that problem, but I guess dissing a technology that is not theirs is much easier than providing a better option.