^ This is as good a guess as any. Maybe something akin to military strategy? Perhaps Sony sees the USA market as being lost to them already, what with Kindle and Nooks. So instead of waging a futile effort in a major way, they shift their primary focus to other global markets, where ereading hasn't become quite as engrained/popular...yet.
The world is bigger than USA after all
This would fit nicely with the recent announcement from Sony about pairing up with [? company forgotten] in this area, possibly only for Japan/Asia.