Not for portability. Do most Windows users have PS viewers installed?

That's right. And that's why I did not write it as my own opinion. 'Social' reasons make pdf better in this regard.

I still prefer html for reading on-screen, though.

I should point out that the article is incorrect. Namely, PDF is a complete superset of PS. Furthermore, it is capable of supporting non-printer specific properties like digital signatures and even external files and animation, none of which are supported by PS. (And before you say that animation is useless, imagine using PDF for presentations). Try reading the PDF 1.6 standard sometime (its dry like all standards but it gives a demonstration of what PDF is capable of).

Are you sure that PDF is a superset of PS? Which parts of PostScript are part of the Portable Document Format?

I'm not familiar with the new stuff in PDF/PS but I'd say it probably depends on the specific versions. At the very least anything that adheres to EPS has always been part of PDF.