The only reason flash is blockable is because other web technologies, primarily open ones, have limited the need for it. If no attempt was made to match the feature sets of closed, single vendor plugins like flash, realplayer, QuickTime, ActiveX etc, then the majority of the webapps and media sites would be made using those tools. I think the same is true for games now. Do you really want every game engine developer to have their own plugin, with all the security vulnerabilities that will entail?