In a society with strong diversity, you design the system to be flexible enough for everyone. Often it means to find the sweet spot where you maximize the experience and the access whatever your requirements are. The work of Web standards is part of this system to maximize the experience.
The mobile devices are bringing a lot of diversity to the Web world. That is good. It should encourage universal design, respect of Web standards and not designing systems for specific systems. Unfortunately, Web developers, designers are being caught in the way they designed past Web sites : Desktop designs. The experience is then being very poor on a mobile device.
Their first incentive is then to design yet another entirely new site that will be specific for the mobile. That is a mistake. Browser sniffing stinks, even more so with the mobile era. It’s a sisyphean challenge. Every year, new handsets, new specific browsers. Willing to sniff Webkit user agent string? There is no Webkit on mobile. The list of user agent strings can be daunting. And the future with the rise of mobile in North America, the tablets and ebooks readers will be colorful.
Design your Web site for any devices. If you want to create an experience on the mobile, then design specific applications for mobile devices. APIs should help here.