actually you are right but upto some extent.. ya reservation counters can fill the names before hand but than they can't book all the tickets in 10 seconds...
the tickets getting sold out due to modification..
if you go to modify a booking , they only need to change the date of the previous ticket already booked...
so now a days the clerks...
more... book waiting list ticket in advance and when the PRS open they just modify the date wit the current ARP...
within 3 seconds a pnr with 6 people can be modify... and you will get a confirm ticket...
I have seen this n I am 100% sure of the technique...