Just because it has 512MB reserved for the OS it doesn't mean that amount of RAM is not included in the specs. You can't asume that they are using an extra 512MB of RAM for the OS. And rumours say that it will have 1.5GB of RAM in final hardware.
You misunderstood - I was saying that the extra 512MB is still there, whether it's reserved for the OS or not. I wasn't assuming that it was 2GB RAM + 512MB RAM for OS.
But then, there seems to be multiple rumours. I also don't understand why the rumour with 1.5 GB of RAM (which doesn't claim that any of it is dedicated to the OS) has been merged with the rumour with about half a gig of RAM being dedicated to the OS. The latter came from an Ubisoft employee that said that the Wii U would have 2 GB of RAM.
Perhaps some wires got crossed along the way, and the dedicated RAM is part of the 2 GB, bringing the usable amount down to the other rumour's 1.5 GB. Meanwhile, I don't understand why they'd provide 3 GB of RAM in the dev kits, but only 1.5 GB of RAM in the actual system. Including a bit extra, I'd understand - it provides room so that they can get it working first, and then optimise to get it within the available RAM... but surely they wouldn't need twice the RAM, in this context, for that?