The grandparent is saying that if you run plain Ubuntu directly on a device, Ubuntu (or really, the Linux kernel) might not have drivers that work reasonably well for some hardware on that device, while Windows most certainly does have decent drivers for that hardware.
When you run Ubuntu on top of windows, windows replaces/emulates the Linux kernel - at least the part it needs to run the subset of Ubuntu that windows currently can - this emulation provided to run Ubuntu is done on the interface between the kernel and userspace, it is not done on a device/driver level.
Drivers are OS specific, the drivers in question here are either windows drivers, which works only on windows, or they are linux drivers which work only on linux. (Noone is writing drivers for windows which could also work on linux)
Its not a layer on top of the NT system call infrastructure. Its brand new NT system calls that do exactly what the equivalent Linux ones do. There is no combination of win32 NT system calls that will get you the behavior of fork().
Aren't the NT system calls also just a personality module above the actual NT kernel? The kernel was originally designed to provide multiple kinds of user spaces so that it could run OS/2 programs alongside Win32 ones.
When you run Ubuntu on top of windows, windows replaces/emulates the Linux kernel - at least the part it needs to run the subset of Ubuntu that windows currently can - this emulation provided to run Ubuntu is done on the interface between the kernel and userspace, it is not done on a device/driver level.
Drivers are OS specific, the drivers in question here are either windows drivers, which works only on windows, or they are linux drivers which work only on linux. (Noone is writing drivers for windows which could also work on linux)