Raids are instanced too... my guild had this same issue one day for Ulduar 25.

I've had it quite a lot, any time I try to instance during prime time.

I've recently decided to level my odd toons still around 70th, via multibox.
Druid, Priest, Shaman, Warlock and Hunter.
The initial plan was Feral + Discipline with 3 DPS.
And to instance as much as possible; I absolutely detested 70-80 questing.
Unfortunately, I'm getting instances cannot be launched a ton.