"Dual stage" (or 2 stage) means it also has those main augers, but it also has a second feature, an impeller behind the main augers..the augers on a 2-stage turn slowly, "chew up" the snow and feed it to the the impeller..the impeller spins much faster and actually does the work of spitting the snow out the chute..in this photo:
you can see the large spiral pair of "augers" that take up the whole bucket..
then behind those is the smaller "impeller"..it looks like a 4-bladed fan..
the augers + the impeller = the two "stages" of a dual stage machine..
The difference between a snow "blower" or snow "thrower" is more nebulous..
some say one is a single stage, and the other is a dual stage..or vice-versa..
Personally I consider the smaller single stage to be "blowers" and the larger, more powerful dual stage to be "throwers".."Throw" sounds more powerful...but its not carved in stone, there are no "official" uses to either term, that I know of..
the terms are basically used interchangably, and either is used to describe any snowblower.."Snow blower" is the more common term, that describes any machine.
Like Sscotsman says, thrower - blower seems to be whichever one you like. Here the single stage machines get referred to as snow throwers, while the two stage are tagged as snow blowers. Guess people think of the impeller as a big fan that blows the snow.