Each week Ross Rubin contributes Switched On, a column about consumer technology. For many products -- TVs and the iPod, for example -- the leap to color displays represented an evolutionary change. But color was just part of the big leap that Amazon made with the Kindle Fire, moving from a reading appliance to a converged device. There was no couching it as "a reader's tablet", the positioning Barnes & Noble had sought with the Nook, even though Amazon now claims that it has the "best content ecosystem." Still, as discussed two weeks ago in
