Depends largely on how accessible stuff they are used to is, I guess. I saw Joe Bonamassa last month (in the UK), and he had his full four-amp rig with him, as did Mark Tremonti when I saw Alter Bridge a few years back. As far as Opeth are concerned, they had Laneys when they recorded the Lamentations DVD. But I take your point, a lot of bands do use rented backline.