Maybe I misunderstood the article -- it sounded to me like requests were being distributed between Mongrel processes and queued on the individual processes rather than being queued centrally and only allocated to individual processes when a process is free (like Apache does).
The problem with Mongrel is that you allocate N mongrel instances at setup time. Apache, on the other hand, can dynamically allocate new processes (up to a limit) in order to meet increased demand. This is especially important for people like me, who host more than one site on a machine, and want to be able to handle load up to a certain point without fiddling with config files every time there is a spike in traffic.
