An ever growing number of users, especially younger users, utilize their smartphone to browse the web and participate in forums, chats, etc., don't ask me how they manage since my HTC Hero drives me nuts when I have to type more than LOL with it, but that's what the demographics are. Not providing a official mobile style is imho misguided in the light of how consumers want to consume content.
I can appreciate that there is one(?!) 3rd party style, but (and no offense to the creator), from a business perspective a 3rd party style generated by just some guy is entirely too unreliable to utilize in a for-profit forum. So make the official mobile style a paid module, those who run forums for profit won't have any issue to pay for a needed feature when it comes with the promise of business continuity.