Compare it to Twitter limiting your communication to 140 characters. Or Instagram limiting your posts to photos (as far as I know; never used it). Or Vine limiting you even more than Instagram. Or Tinder limiting you to swipes (compared to pretty much every other 'dating' app out there).
In all cases the limitation is rather arbitrary, and yet one of the primary defining aspects of each product. I don't think it's a stretch at all that the ephemeral nature of Snapchat is its main offering. I kind of wish more of my friends would use Snapchat, because I'm not always happy with the idea that everything I ever said to a friend via Facebook is stored and can be read and searched by them. And by Facebook.
In all cases the limitation is rather arbitrary, and yet one of the primary defining aspects of each product. I don't think it's a stretch at all that the ephemeral nature of Snapchat is its main offering. I kind of wish more of my friends would use Snapchat, because I'm not always happy with the idea that everything I ever said to a friend via Facebook is stored and can be read and searched by them. And by Facebook.