I want to get back to the main question: How does GPlay define a device as "not compatible"...
What I have discovered (so far):
GPlay checks the name of the device
Yes, but... Why are most of the APP's declared as compatible (Facebook, GMail, Temple Run2, Skype, etc.)? Only G+ is "not compatible". So the name can't be the key for GPlay. Seems to be that the APP developer defines it.
GPlay checks the hw-features of a device
No, because G+ is good for my son's crapy phone but not for my dual core tab.
Question to those who have a developer account for GPlay:
Which parameters can be set (compatibility) when you upload you apk to the store?