Now that is a topic! (I must have said this thing for at least 10 topics, but still,,,)
Well I dare say that these polls are worthless. In any aspect, but one: I only look at these lists to discover any guitarists that I am not aware of already. Apart from the usual suspects, guitar heroes and gods(EC, has lost his deity status long ago), I think that the rest are there for reasons that are a bit beyond us.
The "contemporary" factor is very important. Q have voted Radiohead 's "OK computer" the most important record in history, a couple of years after its release, and Johnny Greenwood was the new guitar hero, included in every guitarist poll. Any spot of him now, in the new Radiohead records
?
The new tone (unique sound) is something that easily catches the tired ear of the old magazine poll-voter. But many times it is nothing more than "fireworks", a lucky turn of the knob in the amp that did the trick. Edge surely knows about this!
But of course if there are fine compositions that fit this new sound, it is fine by me. U2, up to Achtung baby, produced at least 4 great albums! And even before them, Eric Clapton, Jeff Beck, Jimmy Page, Peter Green, Pete Townshed, Jimi Hendrix, and many others built a career because they were there to use all the technical innovations for guitars, in popular songs. Yes, most of them had the touch as well, but what made them guitar heroes was the combination of the two. The LUCK factor.
Kurt Cobain, is the obvious example, that these polls are worthless. No matter how influential he is, we have to consider why he has become so. I believe that most of Nirvana records were well marketed products, with a bit of the punk ethics that appeal to the young fan base that back in the early nineties were the big consumer target group. Nevermind have some catchy tunes, but apart from that nothing else to show. It is not even their best record! Grunge was the hip thing then, and Cobain's suicide in a way, fulfilled in the minds of the fans the rebellious nature of the musician and his music. Of course all this has nothing to do with the actual music or his skill as a guitarist.
Neil Young (someone mentioned him, as not being that good) is a genius of a guitarist. His time swifts and peculiar pitch is one of a kind. And he is so unique that few can actually imitate him, but since he has sold so much he is influential. Even Kurt quoted him in his suicide note, with a line from "Hey hey, my my", which actually mentioned Johnny Rotten. How about this connection .
When Mark Knopfler stepped in, the rock world was full of guitar heroes, and since punk was well on, guitar anti-heroes. (Who voted for Steve Jones? almost nobody) However his finger picking style was unique but not easily copied. It is a peculiar thing, but the classical guitarists that can actually play fluently all the finger picking style of MK, are somehow snobbish towards Rock music, and only lately, the boundaries between classical and rock music are erased. So yes I do expect many guitarists can play like MK, who actually treats his guitar as a guitar and not like another stringed instrument. Don't get me wrong, I like more technical guitarists, but in a more logical sphere. You might say for Vai "wow, how did he do that" but with MK you just don't care.
I never spotted (maybe because these polls are for rock guitarists) Harvey Mandel, or Larry Coryell or Steve Kahn, Larry Carlton. They have great technical ability, played in many records as session players and have their own followers as well. But they never sold that good, because they were jazz, or too near jazz. John McLaughlin usually makes it, though. Maybe that is the answer for Robert Johnson being so down in the poll, who admittedly has been influencing guitarists for 3 quarters of a century and Django Reinhardt. If MK was the one to suggest the Reinhardt music in "Metroland"OST, an extra bravo.
As for grading systems, I don't see the point. I mean, it is enjoyable to see technical guitarists on stage, but when it comes to recordings, you must have a good composition to lay the guitar. Or at least a fitting one. Listen to Vai playing at Zappa's records and you will know what I mean. By the way was Zappa included?
And yes the Andy Summers example was very good. I guess the same goes for Adrian Belew and Robert Fripp.