They want to be sure that you're not intending to stay. They presume that you are and it's up to you to prove that you're not.
(Although the last time I entered, a few days ago, the way the DHS agent phrased it was merely "You're planning to go back, right?" I answered "eventually, yes", and that was enough for him to stamp my passport and let me through.)
who on earth travels with a copy of their employment contract, rental agreement, etc.?
people who don't have return tickets, that's who.
Most travellers DO have return tickets and that is usually enough to satisfy immigration. It is the one's that don't have a return ticket that are warned to bring evidence of ties to their home country.
As only a small fraction of traveller's annually are denied entry, one presumes that most people who visit the US under circumstances such as yours have thoroughly researched entry requirements and make the effort of carrying a photocopy of their lease with them.
The only HS officer I spoke to was the guy at passport control in Detroit, who just asked me very few questions, stamped my passport and then wished me a nice holiday.
Sshhh...don't let that one get out. It will ruin their reputation.
Don't worry Siduri..you will be just fine. Have a lovely holiday.
