Maybe they do, maybe they don't. 1000W power supplies have been available for a very long time.
My desktop system has a 750W Cooler Master power supply at the moment, and I'm using maybe half of its capacity under load. That's for an i5 2500k overclocked @ 4.8GHz, a Hyper 212+ heatsink*, 16GB of RAM (4x4GB), a Radeon 6970 graphics card, a DVD burner, a 60GB Intel 520 SSD as cache, and a 3TB mechanical drive, on a Z68 motherboard. I could buy a video card with a 500W draw and still have some juice left over.
It's quite possible that the system built 5 years ago has a power supply that's more than capable of powering a modern video card.
* - Since somebody's going to cry foul at using air cooling on a system clocked @ 4.8GHz, I'll point out that I'm using an Antec Eleven Hundred case, with two 120mm vents over the CPU, a 120mm vent under the CPU, and a 200mm fan in the top of the case, which provides more than enough air circulation to keep it cool with that processor/heatsink configuration. Even after 4 days of transcoding @ 100% CPU usage with Handbrake (queued up 60 DVD's to transcode after ripping), the CPU had not exceeded 65'C and was averaging about 60'C.