Valid reason for them is they would have to spend money on supporting and maintaining cross signing. I can image it is much much cheaper to just store priv key.
So if they can get away with it they just do it, no one is there to stop them.
> Depends of your paranoia level: either because laziness or because of evil intentions...
They disposed of the "Don't be evil" promise in a very active and energetic manner, seems like we have rational grounds for deciding, without paranoia :)
Would be nice to get a confirmation of this as it sounds wild.