There are two kinds of answers to this question, well three.
1. Corporate butt-covering and dealership service dept profit from getting customers in for services.
2. People who drive like they stole it, do heavy towing down hills, or just repeat what they read somewhere. They should change it every two years or even more often in severe service.
3. People who realize that brake fluid does not absorb much moisture over several years. That it "can" absorb moisture, and that a minuscule amount can seep through rubber, doesn't mean it's enough to make much difference. These people can wait 5 years or longer.
I have owned my share of vehicles. I have never changed the fluid in less than 10 years (with exception if a wheel cylinder or caliper failed which has been rare on vehicles newer than ~'90s model years) and never had a single problem resulting from it. I do get brake line rust out at around the 20 year mark but this is from the outside of the line, due to salted winter roads.
If you do have a severe duty application and notice undue brake fade, definitely get that checked out and that may be a sign it's time for a fluid change or more. If you notice your fluid getting dark that is the rubber and not a sign you should just replace fluid, rather a sign you should replace rubber if you feel it's excessive.
On the other hand brake fluid is cheap (if you DIY) and a side benefit of doing bleeding more often is that if you are in an area where rust is common, getting the bleed nuts loose every now and then decreases the chances they'll be seized in and break the next time you try to remove them. One thing I would not do is let some kid at a Jiffy Lube do it. You'd be better off not getting it done at all rather than risking a (possibly) incompetent person working on your brake system.