Well, that what you propose is very nice, but i just give you an example, so you can understand that i have no other way.
I'm working in a company that makes games for cellphones, games have common java source files and specific for phone. So for example i have midlet.jpp at common source, and for phone Sony Ericsson k790 this source is working fine, but for Motorola Z6 it's not. So programmers here create midlet.jpp for Motorola Z6.
I'm sure that putting defines everywhere at code for all phones will be a mess, i have seen projects like this, and it is very difficult to read that kind of source.
And what's for concurrency issues, i really don't much care, because i will just compile project without starting two makes.
Thanks for your reply