I've got a question related to the original topic from hybridbear. We've got a 7 month old Fusion Hybrid SE with 11,000 miles and a 2007 Toyota Camry Hybrid with 120,000 miles. While the OP seems to be drawing similarities between the Fusion and Prius, I've found the Fusion and Camry to behave considerably differently. Is this really the case? No Prius experience here but I'd expect the Prius and Camry to be similar.
No Scan Gauge, but my observation of the Fusion operation is in agreement -- the ICE tends to either work hard or is off, maintaining most efficient operation (I'd presume). It is constantly cycling on and off, indicating either EV operation or low MPG. Speed limits (and my driving) rarely exceeds 65 MPH. The ICE is aggressive at cold start, charging the battery and quickly warming up to allow EV operation even in cold weather.
The Camry ICE seems more willing to run at different torque settings, even at lower speeds (<40) which allow EV operation. You have to work at getting it to cycle. It really seems to just want to use the battery for load balancing. The MPG gauge will easily maintain about 40 MPG constantly with a steady cruise, something the Fusion just will not do naturally. In freezing weather, it often refuses to enter EV mode at all. I wonder if this might have something to do with the NiMH battery limitations compared to the Li-ion in the Fusion? The NiMH batteries tend to lose capacity over time at a faster rate, yet fuel consumption doesn't seem to go up. The Fusion seems to have a larger battery reliance (although as you post, it, too, uses very little of its capacity) which might not bode well at 150,000 miles or more.
(As an aside, we are getting 5-10 MPG better with the Fusion, plus it's a much nicer car in just about every respect.)
There are a lot of differences in the programming. The Prius & Camry are very similar. Toyota, Ford & Honda have all taken difference approaches to the programming of their hybrids. All achieve roughly the same gas mileage. Time will tell which system is the best.