I agree entirely about hydraulics, and yes, it makes a huge amount of sense that a big truck would need something other than an electric winch. You can multiply up the torque of any winch by using a snatchblock (or more), but then you need to run the for winch twice as long under load (or more). So even a small electric winch with a moderate current draw would be entirely unsuitable for a bigger truck.
Musky's right about the MM being very different to the electric wnches I have seen. I couldn't find the link, but on one of the boards there are pictures of an H12000 being disassembled - very impressive innards! And as far as the necessary horsepower is concerned, I have never had to have the engine at anything more than idle to run the winch. Of course, the MM is known to be slow, but it's hardly an issue - it just pulls at a constant speed, all day if necessary. I also went for hydraulic despite all the dire warnings that it wouldn't run without the engine running. Other than the "stuck in a raging torrent" scenario (which is definitely to be avoided when solo anyway), it is hard to see why it would ever be essential to winch before getting the engine running.
I'd have thought any hydraulic winch would be lighter than a similar spec. electric winch? An electric motor is massive compared to a hydraulic motor, and the rest is theoretically the same. If my quick and dirty calculations are correct, the 5500kg capacity of the H12000, pulling at 0.03m/sec under full load, works out at a bit over 1.6kW. An electric winch doing similar useful work at the same speed, would be pulling around 450A @ 12V, so drawing more than 5kW!
(This also explains why no revving of engines is necessary unless you have a pump that is too small: at idle, a couple of kilowatts is hardly noticed. In fact, even if you do rev the engine, the winch doesn't pull faster or harder - the bypass valve just opens because it's already pumping as much fluid as it needs.)