Keep in mind that the performance is based in packets per second and the data rate is based off 64 byte packets.
Some excepts:
Model PPS Mbps
870 25,000 12.80
261X(XM) 20,000 10.24
ISR 2811 120,000 61.44
So how is it your your $50 modem can handle a 24 Mbps ADSL2+ connection and a massively expensive Cisco router can only handle 12.8 Mbps?
Well assuming that the MTU is 1492 bytes over an ADSL connection, and Cisco 877 can do 25,000 packets * 1492 bytes * 8 bits in a byte = 298.4 Mbps. Obviously that's when interface speed starts to matter. So really, for maximum download speed over an ADSL connection at 24 Mbps, all you need is ~2010 PPS. 12x less then a Cisco 877 which at $450 AUD on eBay, is only $37.50 for equivalence. I might also add, it won't lock up from too many P2P NAT translations either...
Of course it's a little more complicated then that, but this example helps illustrate why consumer routers are so cheap comparatively
