I disagree--the differene is between tolerances and stocking levels. A lightly stocked reef, with proper water changes and dosing, is much less maintenance than a heavily stocked FW tank--and FW tanks are more likely to be heavily stocked. It takes fewer water changes (larger volume--45% every other week versus around 30% weekly) for the SW setups than the FW, and that keeps the parameters all inline. But--compare a 55 with 5 brichardi, one chocolate pleco, 3 whiptails and 2 bristlenose to a 120 with one bicolor angel, one blue damsel, one mandarin, one yellow tang and ~150 of liverock, fed maybe every other day, lots of snails and other cleaners. Even comparing the FO (one trigger, one burrfish, one angler, ~150 lbs liverock, very few cleaners) is ridiculous--the nutrients being imported with food is hugely different between the 2 systems, much less comparing the non-fish biomass.
Obviously there are different opinions, but what it comes down to: a SW setup certainly doesn't need to be any more work than most FW setups. Planning, careful choies, and regular maintenance adequate to the system will work for either type of tank with little difference in time.