Does that mean Linux will crash?
There are certain assumptions that HyperV make about the underlying OS.
My guess MS are just covering their own, as they don't want the world to know they can't make a decent hyper visor either, or they royally screwed up their assumptions on how the world works when designing the hyper visor... or something to that effect.
Or they recognise that Linux (and other FOSS OSes) are not going away, and if they don't support Linux, then other vendors may look elsewhere for VM technologies (VMWare, Xen, Sun, etc) if they need to run Linux within the VM.