It's mostly about posession of gear, not about cleaning.
we could wash dishes by hand, but we own dishwashers... :scratch2:
Just to be picky

I can build a brick wall and set the brick by hand and check for level by sight, but I will have a much more level top to my wall if a use a simple device called a level.
For some people it may in fact be just having the gear...but just be cause something that we us a machine (device) for, can be done by hand does not make for a logical argument that the machine is not better.
None this has anything to do with the efficacy of any particular record cleaning method.
OK....
Now to the issue of running water. Think back if you can, to one of the ways gold was extracted from streams back in the day. The miners built a sluice box, basically a wooden tube with groves in it to catch the heaver gold as the material from the creek bed was shoveled into the sluice box. Water from the creek was continually flowing in the sluice box. The turbulence set up by the grooves and in some instances bars across the sluice box caused the gold to be dropped out of the running water.
See my picture of a simple sluice box...Anything look familiar? The horizontal grooves in the sluice box and the grooves in a record look a lot alike.:scratch2::scratch2:
Any questions?
Edit: In continuing to think about this...If one held the record horizontally and squirted a stream of water on the underside of the record and could cover the entire underside for long enough amount of time, it might be possible to achieve a fairly good rinse if one did not use tap water. But you would have to have a method of squirting the water on the record. That would be some kind of a machine even if it was a squirt bottle. And it would be a lot of work to squirt enough water on a record with a squirt bottle to achieve an affective rinse.
A vacuum seems to be a lot easier.
And truth be told, one can achieve good results with manual cleaning with enough time and elbow grease. Maybe not quite as good a a vacuum RCM, especially on very dirty records. But definitely much quicker and easier.