Adobe doesn't make money directly off of the Flash runtime (so far as I can tell). They make their money selling the development tools. I don't se any reason why Adobe couldn't re-target their development tools for HTML5 / Canvas / SVG etc.
HTML5 has a lot of capabilities, but developing for it is harder now than developing for Flash. Adobe seems able to create development tools that are approachable by a large audience, why not use this skill to target an open standard environment? They could still be first to market with a killer HTML5 development tool.