Dear Aunt TUAW,
My iPad 2 has an A5 processor. It's got iOS 5. It's super-powerful. So where's my Siri?
Your loving nephew,
The iPad 2 may have a souped-up processor, but Apple has never marketed its voice control handsfree features to the iPad. Those have been specific to the iPhone. You can do a quick google for "enable iPad voice control" to get a sense of that.
For now, Apple's position is this: "Siri is available in Beta only on iPhone 4S and requires Internet access. Siri may not be available in all languages or in all areas, and features may vary by area. Cellular data charges may apply."
There are some hard at work at reverse-engineering Siri to the iPad (and other iPhone handsets). Voice Control was successfully back-ported to earlier units through jailbreak tweaks.
Is Siri compatibility possible for the iPad? Probably so. Does Auntie believe that other iPhone models can support Siri's technical requirements? Yes. Or at least, she believes the iPhone 4 and the iPad line are the most likely contenders for pre-4S compatibility, as Auntie is under the impression that human utterances need a certain degree of digital pre-processing before being sent off to Siri-central for recognition.
Will Siri be ported by Apple any time soon to these platforms? Don't hold your breath.