THIS. IS. AN. EDITION. WARRIOR. LIE.
Sorry, but this particular bit of misinformation has been repeated at least three time in the last couple of days, and I am done being polite about it. Yes, Essentials conincided with several errata, and incorporated those errata (and all the previous ones) where relevant. Yes, it presented alternate versions of several classes, which were fully playable alongside their predecessors. Neither of these things make Essentials a separate edition, especially considering that Essentials was fully compatible with the non-Essentials 4e produces that came before it and after it (and vice versa of course).