I speak for me, but I realized the order was cronological from the moment I got enough rep to cast a close/reopen vote. So, I could have thought this was random from the beginning, or I could still think a random order is in reality a chronological one.
If someone wants to retaliate on people closing his answer, also, he could do it without taking the order into consideration. Ok, casting the first stone means you might have influenced others' decisions, but still there are four more people casting their stones too..so if someone wants to blame the first, he could as well blame the other with equal guilt, and surely doesn't need the chronological order as excuse for his behavior.
Also, there should be a "greater good" to take into account while casting close/reopen vote, and this implies a person casting it is not to be seen as a culprit of something, or a judge, but as an executor of laws. You don't blame the first policemen that arrests you, while thinking his partner is just being led by the first one. You get to know you broke the rules, and the system is taking its action. By whose hands is irrelevant here, being they the first or the last.
I know you could feel a greater burden when casting the first vote, but think that if you do it wrong, others won't follow you (and noone will see your name!), and if you do it right..well, you were right from the beginning and could brag about it :D. And if other people follow you just because they saw you doing something..well, the burden is on their shoulders, not on yours. You did your job, and thought you were doing something good, then the community will do the rest, dealing with its conscience.
As for why this is the chosen order I leave to more competent people to tell.