I wouldn't say tapping isn't considered in the shredding itinerary. As far as most good shredding goes, its scales that are played up and down using alternate picking and sweep picking.

I only think shredding's any good if its accurate. If the right hand's picking faster than the left hand's moving then its sloppy and sounds appauling. Also the ones that just play the scales up and down with no particular order and no feeling sound crap too and on that score I will completely agree with Schmange, but there's no denying that Mr Lannerback et al. add a lot of feeling into their playing, with some good emotive bending, vibrato and melody which is often followed by some well thought out, accurate shredding. That, to me is completely what it's all about and anyone who makes out to be a good guitarist without balancing all these elements is not worth listening to. I like to hear it fast, but I don't like to hear it constant and noisy.