Given the increasing popularity of mobile devices such as the iPhone and Android devices (both of which include full browsers), it should come as no surprise that developers have begun to leverage the various APIs out there to provide mobile mashups that can be implemented without targeting a specific platform or SDK.
MapQuest's recent entree into mobile developer tools is an interesting one. Choosing Android over iPhone means going toe to toe with Google, a familiar competitor to MapQuest on the mapping front. Mapping is logically MapQuest's turf. The company was helping people find directions online before Larry and Sergey were even in graduate school, let alone leaving to found Google. Of course, another way of looking at it is that Android is in line with MapQuest's latest push to open up mapping data.