It's tempting to attribute too much of this to the price itself. Promotion on the App Store(s) can be really tough so a special one-day event like this with coverage from major blogs is extremely valuable. If this were a $5 app that dropped to $2 the developer may have received less lifetime app revenue than he did with this $14->$2 one day promotion—there's a lot of psychological value in being able to get a $14 app for only $2, and only today.

As another data point, so far the only way I've managed to get anyone to notice my app was by making it free (and then it was picked up by all the "free app of the day" feeds and websites, as well as a podcast). I also had a similar "sales" graph:

http://www.syncingdreams.com/2012/03/over-9000.html

Unfortunately my giant spike didn't come with any money since the app was free. I ended up making an extra $40 or so as a result of the "free" day sale (and subsequent 99 cent sale), which is (sadly) a huge spike in terms of percentage though obviously not something to write home about in terms of actual return. I did get a ton of reviews, including some really helpful and thoughtful reviews. Interestingly, even with all the free downloads (which I've read can result in a lot of negative reviews) I'm around 4-5 stars in every region except in Italy where I've been mercilessly panned as a "poor rip-off" of what I can only assume is The Impossible Game (the reviewers there only refer to it as "that famous game").

This is a good point. It'd be hard to measure credit assignment for the success. My guess:

1. Increased exposure: 50%. Buyers got to be reached in the first place.

2. Expiring deal: 40%. This is a close second. Besides establishing urgency to act, it reduces buyer risk without raising value doubt associated with a permanently low price.

3. Lower price: 10%. Lowering the price, IMO, wouldn't have helped much without the increased exposure or the certainty of the price restoration the next day.