Incredible Shrinking Fonts

[Petrus de Calguarium]

Why do the fonts in KDE keep shrinking over time? This is not just in 
Fedora 15, but has affected Fedora in general for many years.

A few weeks ago, I was using font size 12. Then, 12 shrank, so I 
increased the standard system font size to 13. Recently, it shrank 
again, so last night I increased my system font size to 14.

Why does one continually have to choose a larger font size to maintain a 
constant font size?