From the article:
Frank Martinez, a New York lawyer who specializes in intellectual property law and who represents several typeface designers and foundries, said the difference between having a font temporarily downloaded to your computer and having it installed permanently on your computer is like hearing a song on the radio versus getting a band's CD. "Either way you receive the music," he said. "But if you hear it on the radio, you don't own it, and you can't play it again."
If it is WOFF, what prevents one from decompressing and installing it locally?
From http://hacks.mozilla.org/2009/10/woff/:
Fonts in WOFF format are compressed but are not encrypted, the format should not be viewed as a "secure" format by those looking for a mechanism to strictly regulate and control font use.
The compression format is lossless, the uncompressed font data will match that of the original OpenType or TrueType font, so the way the font renders will be the same as the original.
As an aside, I really like more choices of fonts, but the potential licensing cost just drives me away.