Incorrect. Signature is required only of the shipper requests it, otherwise it's up to the delivery person's discretion to either leave the package at the door, at some other suitable place, or leave a note. In general, they don't leave packages outside in 'bad' areas.
Depends on the item. In the US, pharmaceutical suppliers routinely ship prescribed drugs via UPS, etc., directly to patients, including Schedule II products, like opioids. A signature is required by federal law.
OK, whether to leave a package on the porch may be "discretionary" when the item is worth $25, but I'll bet a vendor shipping a $2000 computer would prefer not to leave certainty of delivery up to the "discretion" of the driver. In my business we're frequent shippers and receivers, so the drivers are familiar with our workflow and we've seldom had problems of that sort. Besides, I'm sure they've figured out we'd yell bloody murder for such an offense and quite rightly we should.