I think it's down to two things:
1) He never really captured what he did live on his studio recordings - I'm not even sure it would have been possible, the bloke that recorded this unearthed album almost managed it, but Rory rejected it for some reason, I dunno... it wasn't honest and pared-down enough or something... sounds honest enough for me, just a bit messy in places! :lol:
2) Live, whether he was playing with a cleaner or dirtier sound, he always "ripped it up"
Even the stuff on Against the Grain came over a lot more aggressive than that album makes out (in fact, the original vinyl mix has a bit more bite and punch to it - that's another one that's been messed with, they even managed to lose a bunch of vocal on Lost at Sea). There are storming "live in the studio" OGWT versions of I Take What I Want, All Round Man, Bought and Sold - I guess they'll be on Youtube somewhere. And there's a Souped Up Ford - wow - not sure that was from the same session.
I think you're right though Philly, the actual music itself isn't that aggressive - it's just the way he delivered it. It was like there was a danger the world might end before we get to the next song, so he'd put everything he had into this song. And he'd just keep doing it for two and half hours or so, hardly any let up.