I will agree, PDF qualifies as a layout language (based on PostScript which was a page description language) and not as a markup language. But with
all of the document markup languages available, it seems kind of silly to keep trying to invent new ones. Especially since there are several on the list that already have free, high-quality, open-source tools available to convert their markup into a variety of output formats.
[My vote would've been for one of the TeX based derivatives since Knuth took into consideration hyphenation, justification, proper typography, math equations, as well as a host of other issues when originally designing TeX. But everyone is on the XML buzzword wagon nowadays ... ]
[edit] ... and I'll agree with Lemurion, from a design standpoint, people who still use Arial or Times (with the selection of free OpenType Unicode-compliant fonts available) definitely need to be sworn at
