This is not a popular view, but I think as developers we should focus on one platform and serve it well, instead of making nearly tolerable apps for every platforms.
Some days I agree with you -- optimization/platform-specific code definitely has it's place (we would be nowhere without it, all the web stuff stands on shoulders of giants on other giants), and targeted building.
We thought "Hey, it runs on everything!" would be nice for our future roadmap...but didn't we say the same about Java?