Seeing CLAMP and Akamatsu titles holding the #1 and #2 slots in bookstores is similar to the situation for much of 2002 and 2003, when Chobits (CLAMP) and Love Hina (Akamatsu) were often in those same slots.
The Del Rey manga titles also did well on the Bookscan over-all trade paperback bestseller list, with three in the top 50 (#20, #28, and #45).
Tsubasa was at #5 on the Waldenbooks trade paperback bestseller list, the highest ranking ever for a manga title, and Negima was #10.
The Del Rey manga line is the first big house to get into manga; it did so through its strategic alliance with Kodansha. In addition to its lineage, the Del Rey line has the benefit of strong titles, and an experienced manga hand in Dallas Middaugh.