How and when are encoding DLLs used on Windows?

I bundle Postgres (8.3.15) with another product as a back-end database. On
Windows, the default build includes a bunch of what appear to be codec
libraries, with names like, utf8_and_cyrillic.dll, ascii_and_mic.dll, etc.
But using Microsoft's dependency walker tool, I see no references to any
of these in libpq.dll, psql, postgres or initdb.

So I'm wondering what these are used for, what executable or library ends
up loading them, and when/how exactly this happens. I'd like to know
whether they're actually necessary, since we could save some space in our
installer by omitting them.