SAN FRANCISCO--The second day of Google I/O was all about the Web as a platform, and the platform is going mobile.

Google announced the stable version of Chrome for Android (download) and, somewhat unexpectedly, Chrome for iOS. Despite both bearing the Chrome branding, they both betray the promise of Chrome -- in different ways.

Chrome for Android bears all the bells and whistles of its desktop counterparts. It's got Google's blazing V8 engine, JIT JavaScript rendering, and many of its modern-browsing features. Sync is finally smooth on Chrome, and minor flaws like the absent password sync are coming, a Google representative told CNET.

Meanwhile, Chrome for iOS does a slightly better job at this point at porting the Chrome experience to iPhones and iPads than Chrome for Android. Password syncing is in place, as is "Chrome to Phone," the ability to send a page from PC Chrome to iOS. It's also got a clever, slick way to swipe through tabs.

So where do they go wrong? Chrome for Android is, simply put, not available to the vast majority of Androids. It only works on Android 4.0 Ice Cream Sandwich and above, and it's only the default stock browser on certain 4.1 Jelly Bean devices -- such as the new Nexus 7.

The problems with Chrome on iOS are not its fault, but at the end of the day, that's not going to matter to anybody. Once again, Apple's iOS restrictions on browsers have prevented a truly worth alternative to Safari from gaining a toehold. A Google representative explained that Chrome for iOS doesn't have access to Safari's Nitro JavaScript engine, and Google wasn't allowed to port its own V8 over, so the company used UIWebView, a noticeably slower alternative for JavaScript-heavy sites.

"We want to try to deliver the best experience possible in the given environment. We will continue to explore ways to do this in a way that makes the product be consistent to the spirit of Chrome, as we have done in what launched today," the representative said.

However, in my half-day tests with the browser, it falls far short of what Chrome can do elsewhere. That may not matter to many, since suddenly all your Chrome personal settings and data are available on iOS, but it's a stark difference.