Eratosphere and copyright

Eratosphere's Musing on Mastery threads routinely allow people to post their favourite poems by living authors, ie, under copyright. Tricky one that - for instance if you look up the Michael Donaghy thread, you'll find a whopping number of his poems posted, which surely Michael's executors would never sanction. Personally my view is that a healthy proportion of a writer's work ought to be on the net, and the more it is reproduced, the better. Several studies show that sales increase due to web presence.