Just one point: this is an app idea that has been executed many, many, many times before. I could find you a half-dozen other examples if I had more time for Googling “self-destruct message app” right now.
Nothing against SnapChat! If people like it, that’s great. But it’s a good example of software success clearly driven by cultural factors rather than the inherent attributes of the app itself*. This distinction is very rarely made when people write about software fads, but it’s important.
* Sure, you can tell a story about design/business model/whatever. I don’t think I buy it.
Sure, I think I’ll tell a story about focus. All the ones you linked to have a bunch of features. Their marketing and proposition is about the serious reasons why you might want to make messages expire.
Snapchat is good for one thing, their marketing and proposition is about fun and fun only, and it’s something no social network big enough to have network effects offers as a feature.
Snapchat’s execution can’t be discredited; what they’ve done hasn’t been done before.