That's fair but you can easily develop for the majority Chrome marketshare by focusing on designing and building your applications on top of the actual web standards instead of Chrome's specific implementations. Probably 95% of the APIs you use in a typical app will be easy to use in a standard way anyway.

WebRTC and some of the more mercurial APIs might be a challenge though.

Most developers probably try to do that. But often they only develop on Chrome, and maybe only have automated tests in Chrome (or not at all...). And then when it then breaks for non-Chrome, fixing tends to get lower priority than new features and bug affecting more users.