They would need the benefits, because Boston is very expensive, if you want anything bigger than a closet in a reasonably safe area. I'm sure, like in any big city, they have expensive housing costs and/or a long commute. Still not a bad salary.
Lurch's manservant probably likes the 'prestige' of working for his highness - LOL - and hanging around on Beacon Hill, a place his salary wouldn't necessarily afford him regular access to.