Zip is extremly good at compressing text so its only during loading you get a memory peek, so why bother with binary data for files less than 100MB
Someone i know made a benchmark comparing collada to a binary format madeby him and got these numbers:
collada size 6 times bigger
collada speed 10 times slower
loading and saving collada 8 times slower
Don't know how exact these numbers are.
If we compress collada files not only it will take more time to decompress the files but we still have to spend time parsing it with java xml apis. If we use a custom parser made with a tool like antlr for example it can take less time than using the java xml apis but i guess its still 2x or 4x slower than a binary format.
In a MMORPG or a game with a free movement world that is being constantly loaded from disk speed is critical. In a FPS this is probably not very important but a map that takes 5 minutes loading is allways better than one that takes 40 minutes.