HTML5 is not the only way to achieve cross-platform. In native world, HTML5 is just "one of them". There are many cross-platform frameworks and you can choose any one you like. Look this report.

Cross-Platform Developer Tools 2012 | VisionMobile http://www.visionmobile.com/product/cross-platform-developer... > the landscape of 100+ cross-platform developer tools

Actually this is a big reason I dislike HTML5 (or I think HTML5 is wrong). Developers don't have freedom on languages and APIs. There are no healthy competition.

And don't forget that web browser itself is a multi-platform application. You can use Chrome and Firefox on Windows/Mac/iOS/Android. These are written in a "cross-platform language" C++.

In addition, most video games are written in C++ so many games are released on multi platforms (Xbox360/PS3/PC/iOS/Android). I suspect most web developers don't even know this...