An easy 3 letter domain is much easier for user to remember and type in by hand if they want to and they tend to stand out, whereas all a style does is "make it look good" but doesn't reinforce ease of visitation. There is a reason that 3 letter domains are rather expensive to obtain, especially if they fit a brand image.
Not everyone wants' a fancy style... they are perfectly happy with a base style and tweaking it slightly. One of the biggest Tundra forums is running what is basically a base XF style (not to mention XF 1.x).