Samsung isn't the only Android device maker promising monthly security updates in light of huge exploits like the Stagefright flaw. Google itself is vowing that Nexus devices will get monthly over-the-air patches, starting with software arriving today. If you own a Nexus 4 or any newer model, you won't have to wait ages for these fixes to come as part of a point release. The duration of update coverage remains the same. You'll get major OS updates for at least 2 years, and security fixes for either 3 years after launch or 18 months after your device leaves the Google Store.
This is an easier move for Google to make than Samsung, since it's patching stock Android and doesn't usually have to deal with the complications of carrier- or region-specific models. However, it's also an important step that could set an example for Android partners that haven't adopted the monthly schedule. Google clearly knows that the platform's overall security suffers when neglectful hardware makers leave reasonably modern devices vulnerable for months (or forever, in some cases) -- this tells companies that they no longer have an excuse.
Photo by Will Lipman.