Not true Duncan. You can look way in front of you and maintain proper position and spacing. The key is to not need to look at the wheel ahead to maintain proper spacing: you can get that from the bodies around you. Staring at the wheel ahead is bad technique. You really do need to be looking up ahead.

And at least for me, slow cadence in a pace-line sucks. You want a fast cadence so any slight change doesn't have as large an effect on speed. Feathering brakes, sitting up high, etc are all valid techniques for maintaining the right spacing.