I agree, that's some high idle power consumption. If I had to hazard a guess, it's the controller aggressively maintaining the charge of the flash cells [1]. Samsung released a fix, not too long ago, for a bug with flash cells losing charge for their 840 and 840 Evo SSD line [2], so I imagine it's a delicate process to get right. Are the other NAND controllers less aggressive and/or more efficient with this process? I don't know. I assume it's the same flash cells as the SATA drives but with a PCIe-oriented controller, so I hardly expect them to lose charge any faster than the SATA counterparts.

[1] http://www.purestorage.com/resources/introduction-to-flash-m...

[2] http://www.anandtech.com/show/8617/samsung-releases-firmware...