A: This is an important development that ALL users of non-Kindle e-readers should be aware of. Follow the link!
B: I see no reason why this development, even if it becomes standard publishing industry practice, should be the end of the Sony reader. You still have access to virtually every e-book offered. And, much as I hate Apple and their policies, the fact that the I-pad and competing tablets all read .epub formats leaves no doubt that .epub and possible successor formats will continue to be widely supported for e-book releases.
Also, libraries have strong support in the USA and doubtless in many other countries, and I would amazed if laws are not passed forcing publishers to accommodate libraries in the e-book age.
And indeed, from the publisher's perspective, such a move might open Pandora's Box, for example additional laws forcing publishers to allow e-books to be lent to friends, and to be resold as used. Publishers are building up a huge reservoir of ill will among e-book readers, and sooner or later such policies are going to blow up in their faces. And they will richly deserve it.