If a developer wants to support a number of browsers, then each browser supported needs to be tested. Its just of reality of software development that you test each platform that your program runs on.
HTML5, C++ or whatever language you want to write your game in, all have pros and cons for implementation, deployment etc. If HTML5 isn't providing a good enough user experience, then choose a different technology. If there isn't a 'perfect' solution, then spend some time choosing the best solution for your needs, being fully aware of its short-comings.
Construct2 suits my needs (I'm using node-webkit and cocoonjs).