I just had a significant amount of work done on my house and the contractors left lots of nails scattered around my yard.
I have a two-part question:
Yes it is typical, but a conscientious contractor will pick them up with a magnet or not let them drop to begin with. Sadly, from my experience, not many workers do. Cost of the nails versus the time needed to pick them up, it is cheaper to leave them.
I would call and let the contractor know you are not content with the nails everywhere, see if any action is taken.
There are a bunch of different ways that nails wind up on the ground, and none of them are really avoidable. They fall out of nail pouches, they'll kick out and go flying if you hit them wrong with a hammer or double fire with a nailer, crowbars send them flying, etc., etc., etc. On top of this, individual nails are really hard to find in the grass, even if you know where to look. I'll usually run a magnetic nail sweeper around when I'm done, but not everyone does that and they won't get all of them. If it's a bunch of them and they're easily visible, I'd mention it to the contractor, but ending a large job with a completely nail-free yard is very unlikely.
It's fairly typical. Nails get dropped, nails are struck poorly and go flying.
Nails are not hugely expensive (modern era - supposedly in the era that they were hand-made one at a time, folks would burn down old houses for the nails, though I am dubious that that is an accurate claim.)
Carpenters are fairly expensive and not fond of playing janitor. If the crew has a less expensive person who is supposed to clean up, it's still hard to find every lost nail. So long as they don't end up standing on their heads they generally rust quietly away after a few years without causing problems.
If you prefer to get more, you can hire someone to use a very strong magnet to sweep the area - but even a very strong magnet won't pull in nails from several inches away, so the ground-sweeping operation needs to be very thorough to come close to getting them all. You can rent "magnetic sweepers" that roll along and cover a fairly wide swath, but they work best on hard surfaces, not grass. I use a few hard drive magnets taped to a discarded golf club ;-)
