Even when the webapp is great? I don't see why they or anyone else should maintain several versions of the same app, focusing on one version and iterating quickly is surly to everyone's benefit.
I realise it's more convenient for Google, but I struggle to believe that's the primary concern when a company of their size develops an app for a platform with hundreds of millions of users.
To me it feels the app is intentionally crippled for some business reason. Perhaps it would be more difficut to target ads in a native app, or maybe they want to push people towards Android. As a user, I really don't care and it reflects poorly on them to produce a substandard experience for their users.
Roll on Sparrow for iOS.
I think this issue boils down to perceived ROI on development costs (and 'push web technologies' agenda in Google's case) rather than quality.