^Not necessarily, if you go through the intermediate step of remuxing
to vob, using mkv2vob and then stream it through WMP12. Of course your network capability to sustain high data transfer rate comes into play - but can be achieved.
I also understand that you can stream copy these higher than 4GB vob files into the FAT32 PS3 drive. Have not tried to find the veracity though.
That said, there is nothing like a direct play and direct plugin without any intermediate processing and transmission of data. That is why I am averse to streaming and/or converting to other formats.
Have a look at this article How To Play MKV Files On Playstation 3
And for anyone interested in setting up a WMP12-PS3 stream-machine a few more AVForums.com - View Single Post - Windows 7 to PS3 Streaming - Help?
( I go with Shark 007 codecs)
And there are many more to confuse you if you search google.