While the timing is interesting... all indications point to Valve and Oculus making their own VR HMDs.
It certainly does seem odd to work so closely with a company that will be producing a competing product, even considering often tossed around phases such as "competition breads quality".
But if you think about it, VR tech is so early in its life that it's not insane for 2 companys to have very different ideas on how to accomplish the goal of VR HMDs. Just look at CastAR, and assume the VR clip-on was real at this time. That's a very different display type then the Rift, complete with its pro's and cons compared to it.
Positional tracking is another thing. For all we know, valve may think a sixsense way of going about it is best while all current indications from Oculus are that they will be doing optical.
Maybe Valve wants to do a dual screen setup instead of a split screen like InfinitEye. Or possibly valve wants to pursue a HMD in a higher price tier with better hardware that costs to far outside of Oculus's pricing goals right now.
I could probably go on with a few other examples, but I hope my point has bee understood well enough.
Whatever Valve announces, I'll be interested to see what their doing.