The success of an app depends upon how consistent it is, performance-wise. It has to be a well-tested app, taking into account all aspects of performance under the most extreme conditions.
A top-selling app is one that works perfectly, irrespective of whether the phone connection is on or off, and also one that ideally consumes the minimum possible CPU and battery power.
An app that constantly crashes will never ever get anywhere near becoming popular with users. Hence, reliability in performance is the first and most important characteristic that goes to make a successful app