Now that we're seeing the Essentials line fleshed out a little more, I think we can understand how Wizards of the Coast wants us to view it.
If you're an existing 4e player, the Essentials line is supposed to be viewed as new build options. For you, the PHB is still the authority and the original book (although yes, there have been lots of rules updates).
If you're not already a 4e player, the Essentials line is what you're intended to get instead of the PHB. For you, yes, Essentials does replace the original Player's Handbook.
Sure, they're trying to have it both ways (for YOU guys it's just new options, but for YOU guys it's sort of a new-ish edition), but I honestly don't mind. I think the Essentials stuff is well done, but I still feel totally comfortable playing my pre-Essentials characters.