Windows doesn't need --large-address-aware to pass our d3d tests, right?
No. Windows also doesn't need it to run plenty of real applications that Wine chokes on. It's worth mentioning that those applications aren't necessarily choking on the same things that d3d10core_test.exe is choking on, though.
Meanwhile Wine needs --large-address-aware to pass our d3d tests with CPU memory hungry drivers, since Wine reserves almost all of the higher half of address space and this deprives Mesa of memory.
Yes. It's more than just Mesa, of course. What makes test_cube_maps() *unusual* is mostly Mesa, in one way or another.