I tried opening Bing Maps UK and I see what you mean. You could change your location to the US, but then you'd lose Ordinance Survey Maps and London Street Map, which I'm sure is not what you want.
I don't have any answers as to why Bing Maps UK has removed Map Apps from their menu. You could try asking Chris Pendleton or Johannes Kebeck about this on Twitter or the Bing Maps Blog.
Perhaps it has something to do with Microsoft gearing up to move everything to Nokia Maps later this year. I don't really know.
In any case, if it's just your own work that you care about, please note that there is a thumbnail map below every geotagged photosynth and panorama here on the site which is a link to the Photosynth Map App, centred on the currently viewed synth or pano.
Or type this from memory: http://bit.ly/photosynthcoverage