Behodar:I don't believe that is correct as people have activate siri on jailbroken ios5 ipad2 devices, which you couldn't do if it was somethng to do with the hardware. Also the ipad 2 has an A5 chip like the iphone 4S. The ipad3 has a better chip in it.
Hence the quotes :)
It's software, but it's sold as part of the device, not a part of the iOS update.
Get your point. Although the ipad 3 was never sold with Siri as part of the hardware, nor was that an advertised feature when it was sold . It has only just been added with IOS6. But I think it was expected to be added as it came out after the iphone 4S.