The web is inherently a social medium because it is easy to share URLs. The common name for this is that sites became Slashdotted, named after the popular site Slashdot that was the first of the sites were posted links could generate massive traffic.
Website traffic is social in that while it has the usual day/night differences in traffic that follows a relatively predictable curve, if an article becomes popular, traffic can spike very rapidly to previously unseen levels. A site that typically gets 1 million page views/day may find that suddenly the usual daytime peak of 100,000 page views/hour (less than 30/second) has suddenly spiked to over 500/second (which if sustained would be 1.8 million page views in the hour). All it needs is an influential site to link to the smaller site, or for lots of different social sites to jump on the link.
In contrast, iPad and similar applications do not exhibit this type of traffic. Partly this is because the apps need to be installed, but also because the apps do not lend themselves to the social sharing of content. Yes, most apps have a way of sending out a URL, but that just feeds the social web, it does not add to the traffic on the servers feeding the application.
The nice thing about this is that it makes it easy to size the servers that the application uses. It also makes me think that the application developers are missing an opportunity …