De acordo com a documentação oficial (http://subversion.tigris.org/svn_1.4_releasenotes.html), o Subversion usa um tal de “algoritmo x-delta” para obter maior economia no armazenamento, e isso vale inclusive para arquivos binários:

“Subversion uses the xdelta algorithm to compute differences between strings of bytes. The output of this algorithm is stored in a custom format called ‘svndiff’. svndiff data is what’s stored in the repository to represent the difference between successive versions of files, and svndiff data is also transmitted over the wire between client and server (e.g. during updates and commits.)

“In Subversion 1.4, the svndiff format has been improved to use much less disk space — up to 50% less on plain text files in some cases. Thus, if you choose to dump and reload your repository, the new repository should be noticeably smaller on disk. (Make sure to svnadmin create the new repository using svnadmin 1.4.) Additionally, if a client and server are both version 1.4 , then network traffic becomes smaller and faster.”