They do consider how it will look past the store—not in the least because Apple products are sold online as well as through the retail stores.
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 don't buy that explanation, as glossy displays are ubiquitous on Apple products aside from the Cinema Displays and matte options for MacBook Pros. They surely aren't assuming that iPads and regular Macbooks are being used in perfect lighting conditions, which is an unreasonable assumption to make for any portable device.
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.
That blog post is comparing a glossy LED to a matte non-LED display. Big difference, and one I know about first hand because I own MacBook Pros with both types of display, only my LED is matte.
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.
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.