That's interesting. I shot a local match this weekend that started with the unloaded gun and mags on a table. After shooting a few targets while seated, you grabbed mag(s) and moved on to one other shooting position. Only one more mag was needed to complete the CoF, but most folks just put their three mags on the table, and left one behind. I prepared to shoot I asked the SO about leaving a mag behind. He thought for a second and said I couldn't. So I didn't. Nor did I argue for all the previous shooters to get PEs. Move along.
FWIW, I found much more range lawyering going on at local USPSA matches than local IDPA. I don't think either rule book is more conducive to that -- it's people who create that.
Sometimes on stages like that it's beneficial to do a tac load before leaving. Start with one extra mag on the table, instead of storing that before leaving, store the mag you used to shoot the first few targets and load the full one if that gives you enough to finish the stage.