two way v. three way speakers


I recently heard some magico mini's at a friend's house. They sounded amazing. And they were 'only' a two way speakers, but they filled the room with amazing sound. So now I wonder, what does the additional driver add, especially when it is the same size as the second driver. For example, the SF Olympica III's have two drivers of the same size. I know that third driver adds a lot to the price, but what does it sonically? Thank you all in advance.
elegal
More drivers are used to accomplish three things (if/when needed):

1) cover the full range of sound that can be heard
2) enable speaker to go louder with less breakup/distortion
3) provide wider dispersion of sound so speakers sound good from a larger set of listening locations rather than a small sweet spot in front.

Having said that, getting drivers to mesh properly for good sound is not easy and seldom perfect.

Most would consider the ideal speaker (which does not exist) to use a single driver to cover all frequencies and have the ability to go louder and clearer than the others and disperse sound more or less evenly in all directions.

Of course, # drivers is just one ingredient for good sound. The overall design and build quality counts. That's how a speaker like Magico works its "Magic".