Siri has no place or use on a tablet. On a phone, which has data everywhere it's useful(In theory).Kinda odd they'd release it without Siri =S.
They must have something in store for the iPad 3 with a new IOS update that includes Siri and much more.
But nobody wants to take their iPad out of their bags and dictate a command and put it away. It just doesn't make sense.
Siri requires Internet in order to function. But not all iPads have that, so some would be shut out. So it wouldn't be a good idea to add Siri...
(I want to be on the record saying I actually don't like Siri at all and I wouldn't use it. )