From what I understand, a lot of the chemical processes involved are things produced during fermentation like fusel alcohols (the ones that cause hang-over symptoms...and make mead smell like rocket fuel/bandaids) and H2S (sulfur compounds produced by stressed yeast). It also allows the aromas and flavors covered up by those compounds to integrate and "return". Basically, aging helps nasty stuff mellow out (though some things need special treatment) and helps the honey character to return.
I think more than anything, this is why it is so important to manage your yeast to make them as happy as possible throughout fermentation. The quality, and subsequent length of aging required, for a mead managed properly is far superior to one that takes 3-4 months to ferment or one fermented at 80F or one with under-nourished yeast.
Something I've learned that helps reduce aging and helps to clear a mead faster, both physically and aroma problem-wise, is to use a lees stirrer attached to a low speed drill and occasionally (once every few weeks without aerating) stir up the yeast cake. The re-suspension of yeast allows active ones to continue fermenting, breaks up any spoilage organisms living protected by yeast layers, and the spent yeast will grab things and re-flocculate.
Sorry I don't know the actual chemistry involved, but this seems to work pretty well to reduce age and increase quality of end product. Hope it helps!