Nadal is no Borg
What some people don't understand about Borg, when he is compared to Nadal so much, is that he was always good at fast surfaces. At 18 he was beating Laver at the WCT finals semi final round. From earliest times he was playing against guys indoors. He played (and got killed) by Pancho Gonzales when he was just 16! In other words he was unafraid of putting himself out there (not saying for a moment that Nadal is afraid - but I am emphasising that Borg was working on fast court skills from the beginning). At the same time he was this amazing athlete who could run at speed all day - which made him such a great on clay. Nadal is been somewhat lucky because fast court tennis is no longer present in the world - there is just medium and slow court tennis.
Hence, the main difference between Borg and Nadal is that Borg could play on fast surfaces. And because of that he was able to grab the channel double - he nearly did it 4 times a row (if he had taken that second set tie break against McEnroe in Wimbledon in 1981 he would have done it).