First, there are a bunch of variables here (life of the product, usage, etc.). But for something as specific as a refridgerator, there isn't that much variation (because people leave their fridge on all the time).
Second, for some products (notably dishwashers), the energy star standards are pretty low so getting just any energy star dishwasher may not save you much money (or it could save you a lot) because it doesn't take much to qualify for the ratings in the dishwasher category.
Third, given those caveats, energy star absolutely makes sense. Let me give you some details (some of this is from the Oct. 2008 Consumer Reports which you can access online or buy the paper copy: www.consumerreports.org).
--15 year old fridge at 25 cubic feet, operating cost is $126 per year.
--new bottom-freezer (Amana AFD) at 25 cubic feet, operating cost per year is $54.
The gap is even bigger at hot-water heaters: 10 year old electric storage water heater--annual operating cost of $526. New heat-pump storage water heater--annual operating cost of $216.
Additionally, the numbers you're looking at are deceptive. Here's why: the cost of energy is only going to go up. Oh sure, it's a comodity. So prices will rise and fall. But the data I've seen says that energy prices may go up 30% from now to next Spring (despite the drop in gas prices). So savings in electricity will actually be higher. And if you have...say...a dishwasher that isn't well insulated, it heats the house when you run it. Which requires more AC to cool off the house during the summer. Or if you get a side-by-side fridge (less efficient), more cool air escapes and it probably has a modest impact on higher heating bills. Finally, right now, you're just looking at the cost of buying the energy. If we every introduce some sort of carbon tax or need to start coming up with programs to deal seriously with global warming, it doesn't matter what you're paying for energy, there will be restrictions on power usage (at least vial non-renewable sources) so that fridge that cost less ends up costing you in a carbon-tax or because in order to run it, you have to turn off other appliances in house at times.
And if none of that is convincing enough for you, the stuff that has the most potential annual savings (between energystar and non) would be things like: Washers, dryers, water heaters, furnaces, and thermostats. Additionally, you probably won't save much money in power on a dishwasher but the new efficient ones use significantly less water (which especially if you live anyplace that has water quality or water access issues) is about being a responsible citizen.
Here's another thought: if you don't want to spring for energy star appliances, look at what you can do to add solar to your house. A lot of places have tax credits to encourage this and with a new house, you don't have the hassle of a retrofit. And if you're using self-generated, clean, renewable energy than you're not paying anything for electricity. You're protected against outages or major energy costs in the future and you're also dealing with global warming.