Yes, but the same is true of Knockout - it has no server-side ajax functionality. I'm looking at the code on the example pages and it's solving essentially the same problem as Knockout (there's even a shout out to Knockout on the homepage).

The main difference seems to be that in Knockout has 'observables' that are part of your view model, whereas with Ractive you interact with your view model via Ractive's functions.