I can't confirm this. In my case(MED 6.873), even when I don't select a single vertex, the apply vertices button is already active.

Maybe, you have to reinstall the program. No idea! \:\(

http://www.puppenheim.org/
http://www.wuerfels-welt.de
Old Game Tutorial: http://www.puppenheim.org/MITutorial.zip
Free Game Editor: http://puppenheim.org/AlienalsWeihnachtsmann.zip
http://www.puppenheim.org/blender_starting_main_settings.txt