Yeah I'm not sure if it's as light, I really haven't compared, but it's h.264 decoding is a little quicker and it supports hardware decoding if you have the hardware for it, and it's the right profile, and right format, blah blah (most new video cards have h.264 video acceleration)
If you do a side-by-side of vlc and mpc, you'll notice the colors look washed out on vlc, which could be fixed with some tweaking.
Either way, both have much better resource management than media player.
Media player does have nice tv-tuner features, though.