Is it really that surprising? Isn't that what the iPad 2 has (and people were surprised then). Obviously it's always nice to have more but the iPad seems to run well with 512. Seems like Apple is upgrading ram when the upgrade the CPU.
On a related note, now that we know that the ram is the same too, there's really no technical reason for Siri not to run on iPad 2, right?
The probable reason for Apple not offering Siri to all iOS devices, besides marketing for the 4S, is probably because it is a service relying on cloud servers to complete the analysis to respond to users queries, so releasing it to 200 millions devices on day one without having a chance to see real use cases or a chance to scale the servers properly would be catastrophic.
About the RAM this is, like always, laughable... How people, usually without the necessary technical knowledge, focus on a technical characteristics without understanding its real implications, but still go ahead and critic them.
Apple isn't stupid, for years they have been pulling Obj-C, one of its advantages (or nightmares for devs) was to have old fashioned memory management, but Apple has been making it easier for the devs, but also pushing all the technologies that could improve the efficiency of software on their platform...
Apple has been an advocate of OpenCL, with the latest iOS devices having GPUs capable of using the standard, but more importantly, now that multi-core CPU are going the be the norm, a technology like GCD.
With Grand Central Dispatch Apple gave an easy way for devs to write their code in ways that would properly use multi-core CPUs, and Apple has been promoting its usage for years (even before multi-core CPUs were in any mobile device).
The 4S, while not a revolutionary step forward, is still going to be one of the most powerful cell phone at the time of its physical release (unlike some mystical techs that never seem to show up when they where supposed to) , but more importantly will have a software library that has titles that correctly exploit its hardware.
The Android platform isn't quite as lucky.
Devices spec are good, and even better than Apple's as time goes by since they tend to refresh their lines faster (which is a game the Android manufacturers are playing between themselves since Apple doesn't seem hurt by it), all that costs R&D, and the user benefits are usually small because the platform is a mess...
With all the fragmentation in OSs, Android devs can't optimize their software for the latest OS version, because they would be turning down a huge chunck of their user base.
Then there is fragmentation in the devices capacities (screens, CPUs, GPUs), the fact that the latest beta versions of the OS aren't distributed by Google for devs, so they are going to have to play catch up after the release of devices (so you buy the latest hardware for a subpar experience... great), and finally the fact that the store isn't able to ensure the return on your investment due to rampant piracy and a base of user less likely to spend cash on apps.
