They never said it wouldn't be coming to those devices. Their servers can barely handle the traffic it's getting solely from the 4S as it is. Can you imagine the massive load they would have if all iDevices could suddenly access it at once? In it's current state, it would buckle for sure.
Siri and Siri's servers are in a test phase and the 4S owners are the guinea pigs.
Test phase my rear end. I would accept the test phase BS that with in say 3 months they allow all iOS devices to use it. We both know it will never be allowed on anything but iPhone 4s and beyond.
Lets see the argument given for the blocking has degraded rapidly. First it was it needs an A5 chips (that was complete debunked. Safe to bet the 3GS could easily run it)
Now it is test phase. That is a load of crap. Apple could easily scale the servers in a very short matter of time.
Lets face the facts the real reason for it is Apple needed some reason to justify the 4S being upgraded for people to buy. All the other facts are complete BS. Apple needed a reason for the fanboys to upgrade from the 4S. With out Siri there would be no real reason so they come up with a 100% fabrication one.