> The same is true of Apple when they ship a new app that does more.

There are often better explanations. GMail is fast. All the time. No matter how much mail you have. That's because it runs from a local database and all server interaction is abstracted behind sync and local accesses to data. Google Play is slow because it is a REST app with a native app veneer. It's harder to make an app like Google Play use sync'ed databases. So sometimes it does puzzling things like taking tens of seconds to go to the next track even when you are shuffling only your downloaded music.

Fast apps can "do more" and remain fast. Slow apps are slow for architectural and algorithmic reasons rather than because they "do more."