Well, you don't actually need the machine to make the machine, so to speak.
You need the manual (or even automated) capability to make the basic machine parts, to make the basic machine, which makes more accurate machine parts for the more accurate machine, which will make the more accurate machine parts...ad infinitum. Kinda like the way things have progressed since monkeys utilised the simplest of tools
RepRap is still in the infancy of it's evolution, but certain engineers such as 'nophead', 'Vik' and Dr Adrian Bowyer are making strides toward an affordable platform, attractive to the 'tinkerer' within most of us.