Fragmentation is definitely not that kind of issue. It has to do with Hardware Acceleration, Screen sizes, Memory capabilities, native I/O threading and the likes. The only fragmentation issue I've ever had that directly concerns the UI is the presence of default Android Icons and fonts. Some manufacturers remove them, others decide to not implement them or give them arbitrary layout constraints: Sense UI for instance refuses to let you draw a Generic android icon over less than 40pixels. Motorola Xoom's default OS on Honeycomb did not let you display a size 106 font. Stuff like that.
These are the kind of fragmentation issues you're going to have to bite.
Fragmentation over whether a phone has or doesn't have a menu button is of no relevance. This app(1) for instance works both with the Action Bar, the software menu button and the hardware menu button. I only had to point the onCreateOptionMenu method to a single XML, and the ICS SDK did all the defragmentation work for me. It works fine from Froyo to Ice Cream Sandwich, on tablet, on phone, on KindleFire.
These are the kind of fragmentation issues you're going to have to bite.
Fragmentation over whether a phone has or doesn't have a menu button is of no relevance. This app(1) for instance works both with the Action Bar, the software menu button and the hardware menu button. I only had to point the onCreateOptionMenu method to a single XML, and the ICS SDK did all the defragmentation work for me. It works fine from Froyo to Ice Cream Sandwich, on tablet, on phone, on KindleFire.
(1) shameless plug: https://market.android.com/details?id=com.fairyteller.icanre...