Okay, so they are "saving" all the 666GB/platter drives for the 2-3TB drives?
Yeah, this is my understanding. But maybe WD has more to offer than I know. They're not transparent. And I haven't bought 3.5'' drives lately. I'm not seeing any 1.3T drives on the market anyway.
And many 1TB drives are 2 platter?
Only old ones should have more than 2 now. But you never know with WD. Samsungs is talking about bringing single-platter 1T 5400 rpm to the market but until then, yeah: if you want 1T or even 750G, you'll need two platters.