I'm using Windows 8 RTM 64-bit,
Why only the default browser opens up in metro-style app? If IE 10 is set as the default browser then it opens as metro app and Chrome opens only as a desktop app and vice-versa if Chrome is the default browser. Why can't both browsers open as metro app at the same time?
You can change IE default open in metro style or desktop in this method:
Choose how you open links:
1 “Always in Internet Explorer” will open link in metro style
2 “Always in Internet Explorer on the desktop” will open link in desktop
TechNet Community Support
Microsoft only makes one browser, IE. If you want a metro based browser from some other company, post your query on their support boards. They would have to release a browser version that would run under metro as an app and release it in the app store (like apple, driod, etc). I am sure there will be more coming once windows 8 is actually released to the public in Oct.