If you recall, once a developer had submitted a "Mango" 7.1 app to the Marketplace, it essentially cut them off from access to the non-Mango 7.0 version. That meant that the pre-Mango version was frozen, basically forever, with no chance for bug fixes. And although the goal is to get Mango on 100% of the devices and basically all the updates are rolling out now, developers were still a little unhappy about that limitation.
Microsoft of course listened and figured out a way to let devs have access to both 7.0 and 7.1 versions of their apps. They announced this awhile ago but it has just officially been instantiated in the developer AppHub, meaning devs can update their old pre-Mango apps just like before.
As you can see from the image above, thanks to our developer Jay Bennett, devs will have the option via a drop down menu to choose which app to modify. Seems like a good solution to us and hopefully devs will take advantage of it.