Hmm, I can be a little bit like your DH, but (hopefully) with a little bit more consideration.
For insight, the reason I'm like this is because I bear the brunt of the responsibility for cleaning and tidying, and its an anxious thing about not wanting mess to build up and create a "job" of tidying up, that I don't really have time to do. The house being permanently tidy and "guest ready" makes me feel calm. When I see clutter, I simply see a job that I need to do, and that stresses me out.
So whipping things away while you're still eating/drinking is just rude. But getting up and clearing the table/loading the dishwasher as soon as dinner is finished rather than just leaving dishes on the table or piled up in the kitchen is just sensible. Why dump things on the side and create a job for later, when things can go straight into the dishwasher - job done.
The lanyard would annoy me - why not take it off and put it away straight away. Why dump it somewhere else, and create the job of it needing to be tidied away? And whilst the lanyard is just one small thing, if you do this with other similar things as well (coat, shoes, umbrella, handbag, car keys etc) and multiply that by several family members then all of a sudden you've got a load of clutter than needs the "job" of tidying up - when it could have be put in the right place straight away, no tidying up then required. That said, I'd never follow someone into the loo to complain about it - that's just odd and rude.
The school books. If you were mid job, and just popped to the loo etc, then of course it's fine for them to be left laying around. But if you've decided to stop work for now, and maybe come back to them in an hour or two, I'd expect them to be tidied up at least, rather than left strewn around. So a neat pile on the desk/table fine (not put fully away or taken out to the car), but expecting other people to work around a big pile of clutter for a couple of hours - inconsiderate.
Children's toys - the rule in our house has always been to tidy up one game before starting the next. So if they're painting, the paints get put away before they get the lego out etc. Obviously they can play with more than one item at a time, but if they've finished one activity, that gets cleared up before the next one is started. I would think that's fairly standard, and a good way to start to teach children to tidy up after themselves.
I think your DH is going too far. But could you not make a tiny effort to tidy up after yourself and not create jobs for later? Put things away as you go, and then tidying up virtually never needs to be done.