[maccman]

This is just as true for client side upgrades, for example in the App Store. As an app developer you're upgrading every client out there, and it's much harder to revert.

Just as you test on the client side, you should have a staging cycle which tests releases before you deploy them.

[jules]

The advantage you have as a web or app store developer is that if you make a mistake, you can always correct it by shipping a new version. Just imagine the stress that's on the Windows Update or Chrome update teams. If an update to Windows Update itself or to Chrome update itself turns out to be wrong, millions of users could be stuck with a non-upgradeable piece of software and each user would be forced to fix it manually.