OK, I feel like an idiot for not knowing the answers to these questions, but it's never really come up before now.
My setup:
office: Cable modem -> pfsense -> gigabit switch -> 802.11n AP, voip adapter, 2 workstations
bedroom: gigabit switch -> 802.11n bridge, 1 workstation, 1 fileserver...
toddvj ftw. Regardless of what the OP thinks the machine can do, I fail to see what is at all impressive about adding a video card and 3 monitors to an off the shelf machine. Looks like any pre-built machine + any 3-monitor capable card + 3 monitors = GAMING BEAST. Ok, that point has been beaten...
Think of it more as a coupon than a gift certificate. And 80% is nearly the highest discount (I think they hit 90% at times, but can't remember), but they do this promotion regularly enough that if you don't get something you want now you won't have to wait very long.
Kids...er...I mean, young adults..don't always have $50 more to shell out for a toy. And they also don't regularly buy food, toilet paper, gas, or other staples. Therefore, requiring an extra $50 could be quite a hardship.