Skin Game came out on a Thursday, so did Cold Days. Changes was released on a Sunday, Ghost Story a Friday, Turn Coat on a Sunday, . Didn't feel like finding more.
Not sure where you're pulling that from.
Skin Game: May 27, 2014: Tuesday.
Cold Days: November 27, 2012: Tuesday.
Ghost Story: July 26, 2011: Tuesday.
Changes: April 6, 2010: Tuesday.
Edit (cuz you cited it): Turn Coat, April 7, 2009: Tuesday.
These are publishing conventions for the past few decades. New books and video home-releases (from major studios—indie releases are more random) come out on Tuesdays. Most video games, too. Maybe you're looking at the audiobook release dates? Because those always come after the book is out, usually on Fridays, though there's more wiggle room, and with their rise in popularity, they're coming out closer to the initial release, sometimes at the same time.