We discussed this issue during Leo visit to Brazil. The idea is that we can provide the "logic" of grouping exclusive buttons and then use that logic when implementing the actual buttons.
The result of this discussion was the two components: Checkable and CheckableGroup. The idea is that any component that needs the feature of being
part of an exclusive group can use the Checkable inside. In the repository a simple example using Checkable with a MyButton item and explicitly using CheckableGroup to handle the exclusivity.
In the MeeGo side, Button was converted to use Checkable inside, and ButtonRow / ButtonColumn positioners were added to hide the complexity of CheckableGroup from the MeeGo API. This approach was justified by the fact that the common usage of MButtonGroup (the meego counter-part of our CheckableGroup) was mostly associated with a LinearLayout; and also the fact that the layout affected the images used by the buttons, so some kind of container widget was needed. If more advanced usage is necessary, it is easy to just use CheckableGroups directly with the Buttons.
The code is already in mainline, commit d090ccb350b344c175115a90602063b10bbc89c5 and the following ones