As nitewulf posted - it also aids coherance
In a "good" 2-way design, the design of the drivers is where the "money" is spent. They usually have a more comprehensive frequency response than what a 3-way speaker might employ.
However there are 2-way designs that use a more standard driver - they tend to have "dips" in frequency response around the crossover frequency.
Pro-Ac and Kudos are a couple I have heard that seems to have dealt with this effectively and present a very uniform frequency response over the audible range
RE:
However, the retail prices of the above don’t seemed to represent "good value".For me - "Value" has little to do with the number of drivers and more to do with the sound quality of a speaker - i.e. I let my ears decide for me
e.g. My speakers are Gershman Acoustics Sonogram and the woofer used in them is nothing fancy to look at, but it is an excellent sounding speaker. It is obvious that they focused on sound quality - and not looks.
Cheers - Steve