This whole conversation seems to be predicated on "pixel" as a unit of
measure. Although it is true that current browsers interpret images as
have a width and height measured in pixels, measuring anything in pixels
should be considered a temporary hack to be repaired as soon as possible.
Others have already pointed out that FIG will use real-world units. I
don't think it would break any rules if browsers also interpreted current
html images, rules, etc. as being measured in printers points (which just
happen to by 72 per inch, a nice match to a typical 72dpi screen
resolution) rather than pixels. If a user wants a different scaling, a
"lens" mapping (applied to both text and images) is appropriate.