It's not like they're making money from flash player. They're making money from content creation tools (i.e. Creative Suite). At this point it may be a bit easier for them to create Flash content but adding HTML5 to that mix should be doable. They are already creating native iphone apps with Flash authoring in CS5 (see http://labs.adobe.com/technologies/flashcs5/appsfor_iphone/)
Content creators will want to create content that is accessible to a wide audience with a good user experience. They will buy the tools that will allow them to do so efficiently. If that means HTML5 then that is where the money is and that is what shareholders will demand Adobe to support (follow the money).
Furthermore HTML5 over Flash makes a good argument for people to buy upgrades to their Content Creation Tools. So there is even more money to be made with HTML5 for Adobe.