Are you still making changes to the barbarian, or is the playtest over for those purposes? I really don't like the way that rage strike is set up. It means that I will need to add a note on all of my daily powers to remind myself of how much damage they do when rage striking. It's like turn undead in 3.5, requiring me to look at a table to figure out what I need to do.
Good point what they really should do is have the alternative Rage Strike option written into the Daily powers.
Now I can see why you might go with a separate power in a book, because.
a) One table saves repeating the information countless times, thus leaves more space for other stuff in the book.
b) You don't have to remember to add the Rage Strike damage bonus to new powers introduced in the book of Primal Power later on.
c) One place to errata if you need to change the damage values.
But with DnD Insider and the character builder I think it would be a really good idea to included the information with the Barbarian Daily powers on the character sheets power cards, and in the Compendium. Where space isn't an issue.