Where did you get the rumor that Amazon tablet will have switchable LCD/ b&w eInk display?
From what I've been reading, it seems that Amazon tablet will be like Nook Color. Some blogs says that it will have Advanced Fringe Field Switching lcd display, but that's just a technology for LCD, not implying switching between e-ink and color lcd. It's like saying iPad or Nook Color has IPS lcd displays.
http://en.wikipedia.org/wiki/Liquid_...ing_.28AFFS.29