Not only can collectors look at pictures, but they can compare and analyse the statistics of each player as chronicled on the card's back. Children can debate the merits of one brand of gum over another for only so long, but they can talk endlessly about the players whose cards they've collected, trade them or peruse one another's collections. Johnny got some new cards, so the other kids come over to see them after school. The cards are social currency. We think of a medium as the thing that delivers content, but the delivered content is a medium in itself.
Content is just a medium for interaction between people.
The many forms of content we collect and experience online, I'd argue, are really just forms of ammunition, something to have when the conversation goes quiet at work the next day. Social currency is like a good joke. Sure, for a start. Trying to memorise it so that we can bring it somewhere else. He tells good jokes.