I am pretty sure that the new stuff is printed with blue ink.
An actual blueprint has a feel, a fuzzyness of edge of line, its paper is thick, etc.
The paper had to undergo being washed. We just don't have that kind of paper any more. (Well, you can go buy artists paper, like specifically for watercolors).
If you get your hands (or just eyes) on a real blue print, it just has so much more depth in it.

The prints I have seen in stores are printed.