I see MS's lack of having a consistent message continues.

If I buy Halo on Xbox, do I get it on PC?

Maybe, MS isn't sure yet. Give them time, they'll eventually figure it out.... maybe. 

Get a PC bro, wasting your time with Xbox. 

I think this update means 2 things
1. MS made them change it and are going to have some games exclusive to Xbox one so they can sell more hardware
2. They have a feeling that it might fail like games with windows so they just want to make sure that they can back out if it flops.

You would think so but maybe MS really is gearing up to abandon Xbox at some point in the not too distant future. 

I thought that this already was confirmed since Forza + Gears the 2 biggest Microsoft Franchises out-side Halo are coming for the PC.

It comes from being overly reactive and not being confident enough to commit to anything. Grab positive headlines first, then the reality sinks in later. Sounds like Xbox games on Windows 10 is really only meant to help out with game sales for the duration of the time until the Scorpio drops. This already tells me they're going to burn the bridge to the Xbox One sooner rather than later. Scorpio is likely a new gen machine with Xbox One b/c.

Makes sense, I dont forsee MS supporting Xbox One for much longer, 2  years max I think.

Even more reason to not buy an Xbox, yay!