I know it's not the same FEATURE.
It DOES however work the exact same as Siri.
You activate it, you speak, voice is sent to Apple, the information is relayed back.
The only difference is the server I.D ... Dictation has a different IP to assistant.
The very fact that Dictation, which also REQUIRES a data connection to work, is present on WiFi only iPads as well as 3G/4G iPads, proves that the argument that Siri needs a constant data connection is null and void.
If Apple put Dictation on there, which requires a connection, then Siri would be perfectly plausible also.
Quick Edit: noticed your point about Wolfram Alpha ... when you ask Siri in the UK, for example, "Who is Steve Jobs", the info that comes up carries the Wolfram Alpha badge in the bottom right corner.