Short story on why I went 'cross:
So, I started commuting on my MTB. I realized quickly the disadvantages to MTB geometry on long rides (my commute was 15 miles one way at the time), but the advantages in wide tire capability. Alas, though wide tires are great in snow, and even in summer help dampen the ride day in and day out, they are slower.
I knew I needed geometry that was more aggressive, and that I wanted something that was well balanced with narrower rims and tires. 700c is the best category for finding narrow rims, but still offering wide ones. 'cross and touring were the category of bike that gave me wide tire capabilities but kept aggressive geometry for go-fast longer distances.
Between the two I noticed that touring bikes were heavier, the BB is lower, and the wheelbase is longer. Well, some 'cross bikes are plenty heavy, but the low BB meant it would be a less likely good candidate for riding fixie when I convert it for winter commuting. The long wheelbase is good for loads, but my loads are small, and a shorter wheelbase also means more instant power response.
In short, I could go faster, and a 'cross bike would be more overall versatile than a touring bike. I could run it fixie no problem, mount stuff, do some light touring, even ride it in rec. rides on the weekend and actually keep up!
Now, if I were riding 50+ miles a day I would want a touring bike geometry, but the 'cross bike geometry is just perfect for under 40, but it can still do a fast century or long rec. ride! Plus it's lighter!
I don't carry big loads, just light little ones for commuting duty. I do, however, like to joing group rides on weekends. I do like to get to work super fast, treating most of my commutes as a training ride. I do like nimble and quick bikes with tons of versatility.
I bought a 'cross bike, and always will!
Versatility is king.