Matias Duarte is a hell of a designer. He helped create webOS and then brought Android into the consistent, coherent 21st century. So, when he shares his thoughts on Google failing to use standard iOS icons in their iOS apps, it's worth a read. From Google+:
Iconography is an interesting middle ground between the visual emotional and brand elements of a platform and the functional elements. Some icons have become universal, like the magnifying icon for search. Others are strongly branded, like the +1 or thumb up. Share sits in a middle ground where many consider it a brand element of their platform or service, while it is at the same time being so ubiquitous that recognition is important. There's many other "universal" icons in the HIG that popular services deviate from because they feel that their unique spin does not hamper usability and is part of their brand. Consider the Twitter compose button with it's fanciful quill.
In this case, Duarte thinks Android's brand and a standard beyond Apple's trumps the iOS HIG (Human Interface Guidelines). It's a valid argument. Balancing consistency in platform with consistency of brand with aesthetic of designer is a tough challenge. Google has certainly upped their iOS game. Also, the shape of an icon is only one factor in making it discoverable and understandable. Position is another one. Hell, in many places Apple is using text instead of glyphs in iOS 7.
Still, using non-standard icons or processes isn't without drawbacks. It's loud. It's authorial voice. It's greater cognitive load for users. Anything inconsistent, first or third party is. On an integrated platform like iOS, integrating with the platform offers a lot of benefits, especially when it comes to user experience.
If you use Google apps, either a lot or a little, does the lack of iOS-style buttons make any difference to you?