The reason you'd want to use dynamic linking is to ease security fix updates. If a flaw is found in libmpg123 that allows remote code execution (for example), any package that has its own version, or that statically links it into the program, needs updating, rebuilding and repackaging.
Again, at what cost? We have a patch proposed that fixes a real flaw (mp3 sounds bad in Wine.) You all are asking Aric to do more do address flaws that are inconsequential, in my opinion (it takes more disk space than it needs to) or only theoretical (the new code might contain as yet unknown vulnerabilities.)
As always, patches talk louder than emails. --Juan