Of course, many of us have stopped promoting new Google services because we've seen the fate of too many. Among other things, we don't want to have Google's increasingly bad reputation for this rub off on us.
Is that really any different that promoting a startup's product? Somebody has to try new things and shut down a large percentage of them. I'm surprised HN is so against it. Perhaps google should distinguish services that have long term commitments from those that don't?
I think your second sentence has got it: Google is not a startup, and it should distinguish between startup like experiments and things they are making a long term commitment to. And even then G+ shows they won't be perfect, but they can at least try.