This is why you should avoid developing for the Android for at least 6 more months. It has been too liquid and fragmented so far. The yield for your effort is not very optimal.
The Action bar, although in a limited manner, can also be implemented in older versions of Android, so from a coding perspective, there's nothing terribly scary about it.
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...