The reason Lil Wayne gets such high first week album sales is because he has so much hype about him all the time. He has a new song out every week, literally. Eminem (or any of the artists on Interscope for that matter) hardly ever release songs in comparison, and when they do, a lot of the general public still never hear them. I've never heard anybody in real life talking about or listening to Richard, for example.
I don't think Eminem can sell 1 million first week with his next album because, as mentioned earlier on in this thread, hip hop is doing appallingly commercially now. Absolutely dire. Hip hop songs hardly sell anything anymore, and they have almost no cultural impact. The general public don't know any recent hip hop songs, only maybe Niggas in Paris.
As long as this eurodance domination is still going on in mainstream music, I don't think even Eminem has a chance at a big hit now. People just want nothing to do with hip hop anymore apart from us core fans. Even really popular urban artists like Usher, Chris Brown, Nicki Minaj, etc. simply cannot get top 10 hits with RnB/hip hop songs. They had to release eurodance songs aswell to get top 10 hits.
I think with the popularity of Adele, Gotye, fun., etc. at the moment, maybe hip hop can start making a comeback, but Eminem won't be able to get a big hit until it does, and that means his first week album sales have no hope of coming close to a million, but I still think he'll easily manage 500,000+.