Guild Wars 2 collector's edition pre-purchases of late. ArenaNet's Mike O'Brien took to Reddit earlier tonight to address the issues, and he had plenty to say about retailer reservations as well as the fact that Amazon isn't listing the CE.
The long and short of it is that any retailer that is distributing keys prior to the April 10th street date is violating said street date "and risks losing [its] allocation of keys." That said, ANet can't stop stores from taking reservations, but O'Brien says unequivocally that "a reservation is not the same as a pre-purchase."
As far as the Amazon situation goes, O'Brien explains that the company was simply unable to deliver digital codes at the time of purchase in addition to physical boxes on release day, so ANet has "reallocated [its] units to other retailers." Finally, O'Brien provides a link to some pre-purchase CE alternatives.