The likely explanation, to me, is that professional graphics people (Apple's high-end core market) will set up the environment of the device to be perfect for it (i.e. "studio lighting"—basically the same as the Apple stores) rather than expecting the device to conform to the environment. Glossy is better under perfect conditions.
I would actually argue that glossy displays are not ideal in any lit environment, for the simple reason that blacks just turn the display into a mirror. This is also a problem if you've turned down the brightness in order to save power.
Matte really needs to be the default for any display, with glossy as an option.
Glossy was better. (lcd panels were from different manufacturers, so my results may not apply to every case)
edit: unlike in the linked blog-post, backlight intensity of both lcd-s I tested was roughly the same.
Personally, it's incredibly rare for me to be using a laptop outside on a sunny day, so even if glossy were better in sunlight, I'd never base my decision on that fact. But I can tell you that I did get to compare a matte and glossy MBP of the exact same model in an Apple store, side by side, and saw no significant difference in brigntness.