Anyone who doesn't think Java is used in the field is living in a bubble (citation: http://langpop.com/). Most people I know thinks C# is just a Java ripoff they'd never bother to use. Making something proprietary doesn't make it better.
No one is going to rewrite their Windows Phone 7 Apps in C# for a platform that gets a tiny sliver of the market share. If and only if Microsoft can get the OS onto a phone consumers actually buy will apps follow. If the only people who buy Windows 8 phones are UX designers who believe they know better than consumers, it simply won't be worth the effort.
No one is going to rewrite their Windows Phone 7 Apps in C# for a platform that gets a tiny sliver of the market share. If and only if Microsoft can get the OS onto a phone consumers actually buy will apps follow. If the only people who buy Windows 8 phones are UX designers who believe they know better than consumers, it simply won't be worth the effort.