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
Remember too that what you heard that was "amazing" was not the magico speakers alone. You heard the synergy of the source, the CD/DAC or cartridge/tonearm/table, the preamp, the amp, the cables and the room. All are variables and each contribute. What you heard was a system in a specific room that might be different and less amazing in another room... or less amazing (or more amazing) based upon changing the electronics.

The point... the magico speakers you heard could sound wildly less amazing in a different setting (or better). Regarding the question of 2-way vs. 3-way... get the two speakers into your own setting in your own home in a common system and compare the two side-by-side. Any generic comparison between two speakers is not very meaningful and comparison between two types of speakers (2-way vs. 3-way) is even less meaningful.
My opinion is that if you like the way a speaker sounds you will most likely enjoy it in almost every setting, but the amplification makes a huge difference. I have been more impressed with a pair of Focal 807v speakers powered by a Pathos amplifier than my Focal 836v speakers that are the flagship of the series using my Integra receiver. Apples and oranges, but it did open my ears to how much of a part the amplifier has. I have heard the same speakers using identical amplifiers and the 836v was far superior all other things being equal.
All things being equal a three way is better than a two way, due the three way not sharing mid/bass range in a single driver. But this not the end of the story, driver selection, crossover design/integration and cabinet construction also are important in overall sound quality. And as mentioned by MceLjo, amp choice is also very important, why have great speakers if they are under driven by the amp?
@Maxboy00 - Because you can't afford both! Obviously, there has to be some balance, but I like knowing that my speakers are limited by the rest of my system than the other way around. Just my budget compromise preference.