As someone who has a G1 and is stuck with 1.6 I can say that the record wasn't so great.
This seems to be the main problem I have with Android. It's not fragmentation, its simply abandoning people.
I have an iPhone 3G that my company provided for me, it was released on July 11, 2008. My G1 was released 3 months later on October 22, 2008.
My 3G is running iOS 4.1 (8B117) which was pushed to it officially through iTunes. The latest and greatest iOS.
My G1 is running Android 1.6, which was released September 2009, that means that for less than a year I was graced with the cutting edge updates, and then nothing, no longer supported, discontinued.
That's what's so frustrating, I've played with newer Android phones and the Operating System (now 3 releases more mature) is fantastic, but I'm stuck with a frumpy, slow, buggy OS.
This is what I can't get past when buying an Android phone, how do I get one that's going to be supported for the lifetime of at least my 2 year contract? It seems to be such a gamble, every week there's a new "Best Android Handset Ever." The handset I buy looks obsolete in 3 months, and if it were just my lizard brain thinking so I'd have to just grow up and get over it. The real danger is that the handset manufacturers and the carriers feel the same way, and suddenly my new hotness is old news, and no one seems to care if I get the best software anymore.
So my G1 contract is over and I'll probably drop this phone and switch over to an iPhone 4, at least I'll know in 2 years it will still be supported and function reasonably well.