well. it definitely sucks for the buyer. but think about it this way, if you buy a hardcover or paperback in the store and take it home, it's not like the publisher ships you an updated copy to your house when they revise it. i have many outdated books i've bought several times for additions that included corrections and/or additional content.
but, the book store that allows you to get updated copies for free, or a nominal price, is more likely to get my business! o'reilly media already allows you to downloaded updated copies. purchase once, have it for life. something like that.