Just wondering what the rationale is. Is it that you don't want to force everyone to respec because you think the changes are minor enough that most won't?
Blanket talent respecs are actually very disruptive. The least of which is probably not the thousands of in-game petitions from people asking where their abilities went, asking for spec advice, reporting bugs that they can't cast X anymore, etc. (thereby raising reply times for the issue you may actually need help with) For realzies. And, speccing characters is not as easy and straight forward as many might think it is. Logging in to find that your character has no talents and you must then spend time researching and reading what changes were made in the most recent patch and how to spec can be something that makes plenty of people just say 'never mind' and log out. Not a very fun experience. Anyway, it's a last resort for a number of reasons.