Different skill really. Hendrix was no acoustic player, Zappa never touched one. Jeff Beck? nah. Stevie Ray Vaughan? Nope. They're different instruments, bit like playing a piano and a synth - there's an overlap but their functions are totally different. Starting on one and "progressing" to the other is not really logical. I think a lot of people do it that way because every house has an acoustic guitar lying around somewhere.