You need to know the tempos of the tracks? NO, that's how you do a DMC World Championship set.
The best dj's can do that with any tune with some sort of consistency should they want to. Mixing every tune out after 16 bars would sound dreadful obviously.
Why are you sure other dj's could easily do what Mac 10 does? As I said... go give it a try. Attempt to mix Piano Madness into the No instrumental without writing down the pitches on your PDA or practising it 50 times beforehand. Holding 2 basicly structured 4/4 tracks in the mix for 16 bars is piss easy, yes. But neither of these tracks are regimented, tightly quantised patterns. And there's many more like them.
This topic is illustrating to me how you all can read so much about a genre of music but have no real feel for it, or understanding of what is held in high regard by the people actually within it, as opposed to what is held in high regard by the numerous people blogging about it.
You may have heard a Mac 10 who has hardly done a show in the past 18 months do 4 shows on the Rinse fm webstream with no mcs, but that doesn't mean you have heard what he was doing in his prime on Deja week in week out for 2 years. Also just because you have heard Cameo go to sidewinder with loads of mc's getting really hype on a set and wheel a tune up 6 times then drop the next one in, don't think that is the usual standard of djing.