Nobody can really know, but apparently mens aren't as intense and just come (excuse the pun ) as one "explosion" so to speak (again, excuse the pun ) whereas a woman's orgasm is meant to come in waves.
This sounds like the difference between myelinated and non-myelinated neurones...
If men don't get them so intensly why is it men seem to have sex on the brain more than women? Their orgasms aren't as good so they need it twice as much????