This is great! We need to continue improving how we detect which articles need a lead image - this is in the mobile web team's backlog of things to do.
In the beta version of the mobile site, we actually expose similar functionality (hopefully it will graduate to stable in the not-to-distant-future). If you opt in to the beta site (nav menu -> settings -> select beta), you will see a new item in the nav called 'Nearby'. This uses the GeoData extension (
http://www.mediawiki.org/wiki/Extension:GeoData) to find articles near your current location. You'll note that articles with a lead image are displayed with a thumbnail of that image in the nearby list - if they do not have an image, a camera icon is displayed again (with the intention of making it easy to identify nearby articles missing photos).