Ubuntu != Linux, and More Clarifications
For those not sure, Ubuntu has been a Linux distribution, and not "Linux" itself (which is the kernel). The title of this post says "Ubuntu Does Not Equal Linux" the way you'd see it using the Bash shell. Glad to get that out of the way.
Canonical, the parent company of Ubuntu, has been working towards having their Ubuntu distibution run equally on the Linux or FreeBSD kernels, and now, based on clarifications coming out in various tech news stories, they've been working with Microsoft to run Ubuntu in similar fashion on Windows 10 without Linux.
So, to clarify, this is not a case of Linux-on-Windows. It is actually an upper portion of Ubuntu that will ride on Windows 10 instead of on the Linux or FreeBSD kernel.
For multi-OS devs who prefer just one device, this is not a solution. It pretty well means staying with virtual machines for simultaneous testing on Linux and Windows, let alone on OSX, BSD, Android, iOS, etc.