I never have any problem remembering that I'm readding HN.
I realize I'm likely a very small portion of the demographic, by my prior two decades' experience with Web Annoyances tells me that my own sentiments aren't much different from those of the typical Web user, it's just that I'm aware of, and make use of, tools to fix many of the problems.
If anything, these bars are worse on devices that have poor scrolling behavior, as I've found they tend to interfere with scrolling.
Though, personally I would like pagination (like Google) back for Facebook, Flickr and also Google Images - scrolling down a few "pages" is just buggy on those sites, and click on the wrong link and you have to go back and scroll all the way down!
I Blame it on the design patterns of (Twitter) Bootstrap. A lot of sites are put together with it. Although the default nav-bar is not bolted to the top it is easy to read how to do that in the docs and implement it because it seems like a good idea at the time. Others, not using Bootstrap then copy the 'new convention'.
Personally I believe that for some content, e.g. a Tumblr style blog, the nav-bar at the top (and fixed) makes a lot of sense. If you also have pet-peeve infinite scroll (as many do on Tumblr blogs + Pinterest), then it is helpful to have a fixed header as there is no footer.
One place that didn't work is at Forbes.com because they're using CSS to implement that particular annoyance.