I did a little poking around, and of course, there are federal laws that govern this stuff. According to the
Refrigerator Safety Act, and its amendments, a household refrigerator can't require more than 15 pounds of force to open from the inside. It would be interesting to get a spring scale and hook it to the handles of different refrigerators and see what you find.
Maybe a science fair project in there for the kids.
Edit: Also, an operating refrigerator is harder to open than one that's turned off, because the cool air inside has less pressure than the warmer air outside. Most refrigerators have some sort of venting to try to equalize this pressure somewhat, but it varies by manufacturer how much it is equalized.