I don't understand why iOS users feel so entitled to support from competitors' services. I don't see Apple making Android apps for iTunes, iMessage, or FaceTime (which Apple claimed it would make an "open standard").
And remember that this is a matter of perspective. The lack of good support for Google services on iOS is a good thing for me - it'll increase the number of people using Android, thus hopefully getting me better Android apps for my phone and tablet.
I don't think they do at all. Most of Google's core services are built on top of standards like SMTP, IMAP, CalDAV, Jabber, etc, so they can be consumed by any device.
Apple is the one writing most of the extra code here because they want to make sure Google's services run smoothly on their platform.
While we joke about how crappy it is now, Apple's iTunes for Windows was a good example of playing nice on a competitors platform in an attempt to impress their customers and bring them to your side. It worked.
Well yeah, I'm not quite convinced that it's a winning strategy (or even what Google are doing). But personally, I can never go back to iOS from Android because of the integration with Google products- Gmail, Maps, etc.
Not trying to change your mind, but I personally have a strong distaste for being tied to one product because I use another (unrelated product). It's the reason why I've never bought a song or movie on iTunes. I was where you are a while back with Google products, but email is just email. I don't want my phone purchases to be influenced by what email provider I use; that's just silly. I'm currently using Outlook.com and couldn't be happier with it.
Gmail isn't great on any Android device. If you have only used Android, it might seem great. But after you try the built-in iOS client, your standards will raise a bit (not intending to offend!).
In my experience, nothing that Google has produced for the mobile platform(s) is great.
Seriously? You think the iOS mail client is better than the Android Gmail client? Because... it just isn't. For me, anyway. Each to their own.
Of course Google has made great things for mobile. Maps are unparalleled. Google Now is fantastic. The Google+ apps are actually fantastic, it's just that no-one is using them.
There might be an overarching desire to not make the Gmail experience too good on the iPad.