Webcomics curiosity

Not sure if anyone reading this would know, and I doubt there's any one answer, but I'm curious... Why are so many webcomics portrait-oriented pages? If they're intended for print as well as web and thus fit a standard print aspect ratio*, that makes sense of course, and I can respect wanting the aesthetic feel one way or the other, but... Okay, I was just poking around SmackJeeves, and the aspect ratios were all over the place, some of the stuff there is dojinshi so print would hardly seem in the cards, but everything was portrait-oriented. Why not landscape-oriented, since that would seem to fit a computer screen better?


*Portrait-oriented books are far from unheard-of, but perhaps underutilized themselves.