The ranking is due in part because the publication felt that Microsoft built this from scratch, reinventing themselves. Laptop Magazine considers WP7 as, "an intuitive new platform that pushes the user—instead of apps—into the limelight." They also make note of the inclusion of the Zune player and XBox Live into WP7 as pluses.
Curious who ranked ahead of Windows Phone 7? The Intel Core CPU ranked 3rd, the HTC Evo 4G placed 2nd, and the Apple iPad came in at number one.