kickstarter does not always ended in an aweome-kick-ass product (want a good example? the Ouya ^^) so backers take a risk. The early access was there to give a better visibility, to have more feedback and balance the game, not to design "major" new features, those were already chosen during the kickstarter campaign, so people who buy the game in early access did not really take a risk as "important" as kickstarter backers.
about the rewards, they have the "kickstarter label" it is obviously to thank the ones who trusted in the game DURING the kickstarter campaign. So it would be quite weird to see them in a collector edition.
In addition, offering completely new features in a collector edition might also increase the sells (basic example, I pledge for a kickstarter version which I will offer to a friend and buy a collector edition for me if the collector edition is nice ^^)
