...Except that a lot of the Instrument inputs on these interfaces add 9 or 10db of gain (or less attenuation, it's all relative) compared to its line inputs. This can push hotter pickups into clipping the input circuit. That alone is not a huge deal if you're just going to distort the thing at the amp anyway, but the little bit of "purist" left alive in me doesn't love it. Worse, though, is that you then end up having to pad it back down on the way to reamping. ITB amp sims seem to be coded with this bit of boost in mind, but your guitar amp won't sound the same if you send it a signal that's 3 times as loud. Yes, there are plenty of places to adjust that level on the way, but the only way to be sure you're hitting the amp with the same level it would get out of your guitar is to not change that level!
I record all of my guitars through a buffered guitar pedal (usually my Boos GigaDelay nowadays, but most anything that is not True Bypass works) into the Line Inputs on my machines. If you've got such a pedal, you don't have to buy a DI.