I've been on the hiring side and have spent time with hundreds of resumes and it can take days. Especially in times of economic woe where you tend to get a lot more qualified applicants.
Even with strong well defined hiring characteristics anything past the first couple of passes takes time - or is arbitrary/probability driven.
Let's take your strategy with 250 applicants (and I've way larger numbers on occasion);
* 250 - 1m per resume into yes/no. Let's be generous and say that cuts out 150. At your one minute per-resume that's over 4.1 hours gone already. (I can tell you that 1m is a hopelessly optimistic number. 1m for the people who totally suck. 2-5mins minimum to deal with the amazing number of really quite talented people who completely suck at communicating those skills in a resume.)
* 100 left - at 5m per resume. That's another 8.3 hours gone (and again 5m is way optimistic for a vaguely deep look). Let's say that cuts it down to 25.
* 25 - deep look. That's time spent googling, poking at their track history. Discussing pros and cons with team. That's at least 10m per resume. Another 4.1 hours minimum.
... so thats more than sixteen hours doing nothing but reading and reviewing resumes. Which translates, once you take doing actual work around that, screen breaks, lunch, etc. into probably nearly three days of actual time. For time estimates which are, in my experience, optimistic...
Not that this is an excuse for not getting in touch after a 'no'. If you're getting hundreds of applications you set up a process that can deal with hundreds of applications - but the selection process itself can and does take time and effort. It's damn hard and, in my experience anyway, technical folk foul it up just as much - if not more than - HR professionals.