This was THE WORST idea Blizzard has ever had, to set them on the same lockout. SO, yes. 10=25man. If you kill the boss in one, you can't kill it in another.
Only if by doing the same raid twice each week you could somehow con yourself into thinking you had more content available. Seperate locks was a dumb system, glad its gone, etc.
Now give us more content each tier so we can kill threads like this forever.
Yeah, we totally loved 3.2 with 4 different lockouts of the same raid, didn't we? I mean, that means we had no less than 20 bosses available each week there!
....or DID we?