I can't tell you how many times I've manually read HTTP. To be sure, it's insignificant compared to how many HTTP headers have passed through my computer unseen by me.
ASCII may be inefficient, but computers are really fast, people are not. I don't have any measurements, but in making a browser, HTTP header parsing/writing was never near a performance issue. Bandwidth wise it also tiny compared to that image file you'd inevitably download for every page visit.
And sometimes you don't have tools. Sometimes you don't want tools. Sometimes you want to use tools that work with text to analyse your problem.
(You other arguments might still stand, though :) )