Rihanna can sell that much because she did zero promo for talk that talk And did 200k so if she does promo real good this time and give a kick ass video for diamonds she'll be good!
The only explanation I see is they're doing that because they underestimated P!nk, who also had all the "no #1 albums in the US" pressure etc, and she ended up selling 100k more, so they think Rihanna will do the same.
Also, I doubt Taylor will sell less than 1 million.
I think One Direction will do a bit less....around 450k.
Taylor sounds about right, she might do 200-300k more though.
Rihanna........after P!nk increased so much I would say she could do that, but she's been stuck in the 185-210k range for so long it's hard to see her breaking out.
Diamonds is doing really good on radio, alot of cross-over apppeal and the song isn't as generic as her other releases, maybe that could be attracting people to buy the album
Additionally, she will out-sell Animal by a landslide.