Android's share rises as new phones are introduced, and over time it continues to gain share, because its phones cost less. But when the product introduction front is quiet, Apple quietly takes some share back.
The reason, I think, comes down to two words: battery life. Apple cares about it.
The folks at iFixit have done teardowns on both the iPhone 5, which many friends already own, and the Google Nexus 4 , which I own. Both have specialized Qualcomm power management chips. Most iPhone chips are on two sides of a single logic board, while those on the Nexus cover a larger, L-shaped board.
Last year's iPhone 5 uses a solid Lithium-ion battery that runs at 3.8 volts and has 1440 milli-amperes/hour (mAh) of charge. The more mAh in a battery, the longer it will usually take to discharge. The power drain is listed on the iPhone battery at 5.45 watt-hours (wH).
The Nexus 4 has a battery pack sealed in aluminum, made by LG, but its watt-hour drain is not listed. It too has 3.8 volts and a charge of 2100 mAh. So the Nexus 4 battery should last longer between charges.
But it doesn't.
There are three main causes for a phone's data battery drain the Global Positioning System module, which knows where you are; the WiFi module, whose radio rains data when you're near a hotspot; and software, especially multi-tasking, keeping several programs running at once.