The differences in model, or price points, can be be very subtle. Don't know the specifics on an Itasca, but let me explain some differences in my brand, a Fleetwood Bounder. In mine, I only have a six gallon non electric water heater, but the next unit up the line has a 10 gal gas/electric. I don't have blinds or fans covering the front windshield, next unit up does. Could be a difference in the chassis ratings, 19.5 vs 22" wheels.
Do like Rico says, download the spec sheets from their website, or obtain brochures and compare them side by side. You will find the differences.
Just remember, a floor plan you like is most important, providing it has the little things you want.
2011 Bounder 36R pushed by a 2012 Chevy Equinox