I can use my well pump to run sprinklers. If a submersible works so well then why don't firefighters use them. Are ALL firefighters doing it wrong???? I agree with CDN Farm Boy
I've been watching / reading this thread since the start and I think enough information has been put out here that you now have a basic enough understanding of hydraulics (GPM, friction loss, elevation loss, etc.) to understand the pump output you need for what you want to accomplish so I'm going to leave that alone.
I will second (third, fourth, whatever) the recommendation that you use a larger diameter hose (or fixed piping) to get from your pond to a supply point(s) and then reduce to 1" single jacket forestry hose. With good PSI at your supply point, you can push upwards of 500' of forestry hose and still manage to drag it around (over flat open ground) by yourself if need be.
As to your one question above - the main reason is because the usage conditions are different. You want a pump at your pond to use on site. In your case your pond isn't going to move (I hope). In our case we may draft out of this pond today, a different one next day(week, month, whatever) and yet a third place another day. Additionally they have the ability to "daisy chain" them together to provide higher pressures or to pump longer distances (Relay Pumping).
Having a submersible (well) style pump configured in some sort of portable fashion just isn't practical. At a fixed installation it is.
We have a very large wood mulch plant a few miles down the road from our station. If you are unfamiliar; freshly cut wood mulch has a tendency to "auto ignite" due to heat of decomposition and we get regular calls there for mulch fires.
They have a large pond with a (fixed placement) electrically driven irrigation pump on site. We have keys to the gates and the pump controls and about 95% of the time turning on their irrigation system & calling the owners to come cut it off later is all we need to do. In the interest of fairness & full disclosure - theirs IS a centrifugal style pump, but the intake piping, screens, etc. were installed when the pond was constructed. Unless you wish to do a lot of work retrofitting; then either a floating strainer type intake or the submersible pump seem to fit your situation better)
As FarmWrench mentioned - there will also be the issue of maintenance & reliability with any fuel driven pump system. How often do you plan on running / using it between install and when you REALLY need it? Again an electrically driven system seems to suit you better. In the event of power loss you can use a generator to power it (and I'd be willing to bet you already have at least one - if not I'd suggest a PTO driven one powered by your tractor for the same reasons as FarmWrench already stated).
One last thing and I shall retire my soap box; regardless of what system / components you choose - do not let the fact you have these extra capabilities lull you into a false sense of security. Much like fighter pilots have predefined bailout conditions; you need to decide now and make a "contract" with yourself that if things get to X point, then it's time to go.
Good luck on your project. I look forward to seeing what you come up with.