Wildcard paths were introduced with the FP7 file format to handle converted external data references. I believe this was allowed to preserve references in converted files so that the entire local network would be checked. In my experience, such converted references with wildcards could be extremely slow to resolve. In large multi-file systems, I found myself converting those manually to fixed IP address to improve performance significantly.
Also, launcher files and served files are on different network locations, which means that resolving a relative path will be slow, and isn't optimal as the primary file reference.
The Knowledgebase entry on this (KB ID 771: http://help.filemaker.com/app/answers/detail/a_id/771) notes that wildcard entries from conversion are the LAST of multiple file references to a file, allowing any full IP address to be used for a fast connection unless the direct IP path fails.