The same can be said of fluff; look back to your DMGs, and try to honestly tell me that the Justiciar's fluff entry is any less than, say, the Shadowdancer's. 3.x edition prestige classes only took up more space because of the huge progression tables and ability descriptions(which were, admittedly, slightly more 'fluffy' than the power readouts, but not by much). What is missing, however, is a description of how that Paragon Path fits into the world, but that's intentional; there isn't an order of Justiciars; they're supposed to be PC-specific abilities, things that set them apart from the rest of the world. There's no NPC related fluff because there are no NPCs that do what the PCs can do. What a Justiciar does with his powers is whatever your players decide to do with their powers. They have no footsteps to follow.
LT's white space argument also holds up; the page border in my 3.5 books is about an inch wide across a an 8 inch page, giving roughly 6 inches of writing space counting the spaces between columns. This isn't counting pictures, which have about the same spread in 4E as they did in 3.5. The pictures are just more vibrant in 4E; you still get about one small picture(either in the middle, causing the columns to wrap oddly, or in a corner, blocking 1/4th a page of text) and an image that takes up exactly half of any chapter opener.