It seems that MSE and Stack Overflow (and probably some other sites as well) have one very minor discrepancy that takes away from quick readability of the Page Not Found page.
The MSE version looks like this, which I'm used to:
The Stack Overflow page looks like this:
On the MSE page, "removed from Meta Stack Exchange for reasons of moderation" is highlighted, and on Stack Overflow, it's not. Note, specifically, that I am not talking about the "404" versus an image. That doesn't bother me, since it's not really telling me any information either way (once I've read "Page Not Found," at least).
This is a super minor thing, but I just came across a post on Stack Overflow that I was curious to read and, having under 10k rep, I came across this page. Since I see it a lot more here on MSE (why that is, is anyone's guess), I typically scan only for the word "moderation" in the highlighting, but on the SO version, I had to actually read the first two lines before I realized that it was right there.
There's a big difference, particularly when speaking of meta posts, between "removed for reasons of moderation" and "voluntarily removed by its author," and I like being able to read at a glance which it was. It's not a huge deal by any stretch, but it's handy.
I would like to see the Stack Overflow version gaining that highlight. Again, I imagine this is missing on more than just Stack Overflow (for all I know, MSE is the only site with the highlighting), and I'd like to see it everywhere. I can't imagine this would be a very difficult change to make, but it would save me a bit of time when poking through pages.
Beyond that, for more-or-less experienced users such as myself, aside from "page not found," which is already known to us by the layout of the page, this is generally the only useful piece of information, so I figure as much attention should be brought to it as possible.
Not to mention, speaking just on the principle of the thing, this seems like something where one way is the right way of doing it, so we might as well implement that right way everywhere we can.