Sure, wires and connections can be within the canopy, but ...
Fixtures like the one posted by Electure have but two mounting holes, and those holes do not line up quite perfectly with any box. Instead, there is a separate bracket that is used to attach the fixture to the box. The bracket not only allows you to line the fixture up just right, it provides an entry for the wires into the box.
My fixture not only has a multitude of holes, seemingly placed to accommodate any box .... there is no bracket. Attach the box directly to the fixture, and there is no path for the wires to take.
That's what has me scratching my head.
