The reason I love John's playing (and JPJ's for that matter) really comes out in the live sense when the lead guitarist goes off on one. These guys often had no rhythm guitar or similar to sit behind so have to fill the space themselves. Listening to the shows I have, even when there's no piano, it doesn't sound empty. The basslines may not be the most complicated (Dragon Attack for example) but John's contribution is vital.
And it's a crime none of these lists contain Dave Pegg or John McVie (and that Andy Fraser is so low).