Android 4.0 carried those same concepts further and took them into the realm of smartphones. With its blue-themed Holo motif and sleek new Roboto font, it was arguably the start of the modern era of Android UI for most mobile-device users.
And then Google started to focus on refining rather than reinventing for a while -- a natural and understandable shift. The 4.1 release packed a lot of visual polish, not to mention the launch of impactful OS elements like a card-based search system and the ability to use natural-language voice commands -- oh, and a little thing called Google Now. Later revisions of Jelly Bean brought about elements like the top-of-screen Quick Settings panel, the platform's first multiuser mode, and a ton of important improvements to system-level security.
But those releases remained 0.1-level bumps, as did the subsequent KitKat release -- which, lest we forget, focused on allowing Android to run on devices with as little as 512MB of memory and delivered platform-propelling features like system-level wireless printing and native support for IR blasters, low-power sensors, and low-power Bluetooth devices. It also introduced some extra-Googley elements into the platform, like the home screen design that'd eventually become the Google Now Launcher, and started the move away from the operating system's once-trademark bluish hues (pour one out for an old friend, won't ya?).
I mention all of those specifics to emphasize that those were no small releases; there was plenty going on with each of 'em, ranging from significant new features to noticeable visual advancements. But there weren't any sweeping changes to the core UI -- and the updates weren't full number jumps. See? The full number jumps have generally been limited to releases with sweeping visual changes -- like what we saw with last year's transformative Lollipop or Honeycomb and ICS before it.
Chewing on Marshmallow
So why is Marshmallow -- which, like some of those past releases, packs plenty of significant changes but doesn't feel like a whole new OS -- getting the honor of its own point-zero number?
It could be that Google thinks things like Now on Tap -- a feature that truly could be transformative -- is enough to justify the jump on its own, or maybe in conjunction with Marshmallow's new selective permission-granting system and the integration of Android Pay. One could certainly argue, though, that comparably significant features were included in some of those previous releases, and those didn't get the full number-jump treatment.
It could be that Google wants to distance itself from the negative connotations surrounding the initial 5.0 release, a la Microsoft and Windows 10. That may or may not be the case, but it's hard to deny it as a possibility.
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