tromak:
If I recall correctly, there's "Show Quantity" and "Include Zero-Quantity" values that either one or both of them need to be turned on. I remember modifying a copy of v.1.7.0 to include the <g:availability> tag. I turned both of them on to make it work, but I didn't do extensive testing to see if I could have gotten by with one or the other. I'd probably try including zero-quantity items first if you really don't want to show the quantity in the feed. If that doesn't help, try turning on the Show Quantity option. I think they are both set to 'false' by default. That should do it for you.
I upgraded my Google Merchant Center feed successfully today, but all of my products are still being rejected for the reason that the "availability" attribute is missing. I have "Include Zero Quantity" and "Show Quantity" both set to true, as "Default Quantity" set to 8 in the admin config. However, all those do is create an attribute "Quantity" in my feed with a value of "8".
According to Google, the availability attribute only has four accepted values: "in stock", "available for order", "out of stock" and "preorder".
These are still not being included in my feed, though I don't know what I could have done wrong.
Any help would be greatly appreciated.