The reason is not that Google wanted to leave out the iPhone but but that it was working with Apple to getting GV to work properly. While, they're at it, Google should make it's Google app work properly. It's a good app but not a great one I have come to expect from them.
Perhaps, there will be a combination of both GV and Google's other web apps into one nice efficient app. Simply look at Comcast's mobile app to see the possibilities of what Google's GV, gmail, and reader app can do. Put in blogger, Google, and I'm in heaven.
If you don't know what Google Voice (GV) is, let me explain what I was able to do with it. That might help. I was able to get a GV number, link it with one of my mobile numbers. All calls that goes in and out of my phone shows up GV (option I selected). I also have access to voice mail on my phone or through a desktop browser, I can record conversations (podcasters will love this).
But this is what I'm most excited about. Free SMS. Access it on your phone or the browser. Send from your phone or your browser through your data plan (there is a mobile GV page). So you know what that means right?
Using through SMS will cost you nothing as far as I can tell. That means the wireless providers who has been nickle-and-diming us all this time will not get a penny. It means as soon as the GV app is out in the open, get rid of your SMS plan. Simple using GV's SMS feature and send out your text. Then having it pushed back to you via iPhone's push notification.
So you see now how powerful GV is? That's just the bare surface I just scratched in the description above. It's why a lot of folks are waiting for their invitations from Google to access Voice.
With a similar app like Comcast's mobile app, Google can centralize all the most used services with a swipe or touch. It can even create tabs for gmail, voicemail, SMS, and gTalk. When the app is not running, SMS, e-mails, and IMs can be pushed to the user.
Of course, I'm speculating here but it stands to reason the lack of update from Google stems the amount of work it would take to put togetherl what I'm taking about. Seriously, anything less from Google would be disappointing.
Note: I suppose it isn't a matter of whipping up an app in a matter of hours like Apple would like us to believe. In this situation, Comcast would need to work the backend and make sure things work as it should. Note the October 30, 2008 date on the app. Comcast has put a lot of time into this. There is no mention of push notification with the Comcast app for voice or mail.