yes, im going report this on playdota.eu they are going to fix it in new dota map release and in dota2 too since they own dota and valve. Edit : post not found (#404) :F
And seriously without technicallities - replay is 400 kb savegame is 6mb.
With technicalities - it probably saves
hashtables, unit, player data etc engine data and replay only holds actions and map initialisation (random seed) and the game is "rebuilt" from that. again i might be wrong. there might be a warez version of mspaint added to each gamesave due to tax reasons (HHGTG reference :F actually reference to onthemoon. too stoned
but who cares ^^). ask blizzard.
Also, @up your sig seems mispelled
(and yes i misspelled misspelled hope the universe wont collapse ;( )