Meh...
If the power 'counts as a basic ____ attack' then yes, it is one.
If the power 'can be used instead of a basic ______ attack' then no, it is not one.
I'm calling it a case of shoddy templating. In my game, if a power has the 'use this like a basic attack' rider in any of the various wordings, then it is, for all intents and purposes a Basic Attack.
Looking through the Character Builder reveals several different wordings for the feature. Only the Player's Handbook Magic Missile and Eldritch Blast used the exact wording "This power counts as a ranged basic attack. When a power allows you to make a ranged basic attack, you can use this power." This is by far the wordiest (and most redundant) of the various wordings, and I suspect it was changed for those reasons. Similarily, Eldritch Strike also uses the "This power counts as a melee basic attack." words, but leaves off the unnecessary last sentence.
The Sorcerer's Acid Orb simply reads "This power can be used as a ranged basic attack.". Much shorter, yet, in my opinion, means exactly the same thing. Another Sorcerer At-Will, Energy Strobe uses the wording "You can use this power as a ranged basic attack." This power came from a Dragon article though, which further confirms the lack of a standard template. Oddly enough, the two Invoker powers that came from the same book as the Sorcerer use the "You can use this power as a ranged basic attack." wording, which matches the Dragon article but not the same PHB2 that it should!
Paladins have a "This power can be used as a melee basic attack." as well as a "When charging, you can use this power in place of a melee basic attack.".
The druid powers also use the exact same wording as the paladin's powers. Ditto for the Barbaian's and the Fighter's charge replacing powers. I suspect this is going to be the template that is used from here on out for these types of powers and as I initially stated, they all mean the same thing.
Later!
Gruns