Oh I don't think it's hyped. I think GM has done a very good job being specific about exactly what the Volt will be able to do. Not too long ago they revealed that they had to change the body design of the Volt (which is why it looks much more Prius-like now than the initial sporty concept) in order to decrease the drag and get the all-electric range up to the claimed 40 miles per charge. They're also going to have the batteries under warranty for 10 years, so they'd damn better well last that long.
They've also been forthright about the cost of the car, saying that it might be closer to $40k than the initial $30k projections.
There was also recently a story that Applied Sciences is working on a carbon nanofiber battery that will increase the Volt's all-electric range to 80 miles (potentially for the second generation version of the car). GM has given the company $500k so far, so they're clearly interested in this possibility.
So I think it's safe to believe that GM will deliver on the promises made regarding the Volt, because they've been very careful about revealing when expectations about any feature of the car have changed. The future of the company is basically riding on this car, so they have to be careful about not failing to meet expectations.