I looked around, and I discovered the same thing. Not sure why that would be, as the literature on their site still says Google Calendar integration, as does every recent post about Producteev I can find. I did see that they have a calendar view in the web app now, but I can’t see that they would remove one of their main selling features. What’s more, I can’t find a way in the new Windows app to do any sort of Workspace connectivity configurations. You still need the web app for that, apparently.
The Gcal thing could be an error, I suppose. I may have to contact them to find out.