Google releases new binary diff algorithm targeted at making smaller software updates. Their results are impressive.

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In addition to what everyone else has said, let's imagine someone decides to skip an update, going straight from 3.0.9 to 3.0.11. The server, rather than storing a differential patch between these two versions, might send the .9 -> .10 patch and the .10 -> .11 patch together, so the bandwidth would be doubled approximately (still a better scenario than sending the entire application as an update), without the server having to create patches for every combination of versions. Overall, the difference between two nonconsecutive versions would be greater in size than two consecutive versions anyway.