As someone with a fire science degree, and heavily involved in the fire service with an NGO, allow me to clear some of your misconceptions.
1. Yes, you do need those big rigs. Boston Fire just got a new heavy rescue and its big. Why? Because its a rolling toolbox with equipment for everything from fires to technical rescue to collapse rescue to the jaws of life. You NEED that equipment, especially in a city like Boston. Additionally, engines can park further away, but you need the bigger pumps to overcome friction loss in the hose.
2. Yes, building fires continue to be on the decline, however call volumes are not dropping. Fire Departments are becoming more and more of a All-Hazard response type of agency.
3. In a mid or high rise fire of ANY type, you are reliant on the building's fire systems to a degree. Engine companies hook up to the fire department connection to augment the available water supply of the building's fire pump, sprinklers, and hook up to the standpipe system to provide a water source on the fire floor. As for "firefighters and their equipment become of little value above the 10th floor," you can't be more wrong. Forcing entry on the 20th floor is no different than on the 1st. Stretching a hoseline on the 25th is no different than on the 1st - only instead of hooking to the engine's pump directly, you hook up to the standpipe. Engine companies in high rise areas have additional pump stages increasing to 2 & 3 stage pumps to increase the pressure and allow for the correct pressure on the fire floor.
And if you think that fire departments in the northeast WANT bigger rigs, no they don't. Most departments are constrained by the size of the apparatus bay of 100 year old firehouses - so they maximize what they can for space on new apparatus so they can fit in the building and carry what they can. New diesel engines are also larger due to EPA regulations designed for 18 wheelers. There are some departments that don't care about the size of fire apparatus, but by and large, they're dealing with rural areas where they have to carry the water they'll use.
As for the "firefighting standards organization" others were inquiring about, what you're looking for is the NFPA - the
National Fire Protection Association. Please realize that the standards are not only voted on by the fire service, but also the insurance industry and other member industries of the NFPA.
In short, firefighters are just as important today as they were 50 years ago.