Presumably they would've saved 10%+ of their income for at least 15 years prior to retirement. A single person or someone with a working spouse shouldn't have to work anymore once they start their pension. If they are married with dependent children and their spouse doesn't work then I could see them needing additional income. An E-6 retiring today with barely 20 years would have their pension start at just over $22K/yr. Any officer who puts in 20 years should be able to retire on their pension kids or no kids.
I'm not sure if your comments are based on first-hand experience in the military or not.
In the lower enlisted grades, saving 10% of income is a mighty big challenge. Not that it can't be done, but I'd venture to say that very few are able to do it.
I agree with you that a single person might be able to complete a military career, retire as an E-6/7 and live without working again. When you talk about working spouses, it might not be as simple as it looks (my original point). With transfers every 3-5 years, military spouses often find getting a job to be very difficult. (Employers know they will be gone in a few years and may be looking for longer-term employees.) When they are able to find work, it can often be at the lower end of the pay scale and if day-care is an issue, well....
As for officers, if there is college tuition looming for kids, it's not that easy to get by on just the pension. O-5's and above should have an easier time. But a lot of officers who work their way up through the ranks retire as O-3's/4's - certainly decent pensions but not huge.
Finally, housing can chew up a lot of a soldier's/sailor's/airman's/marine's/coastie's income in areas where there is not base housing available. These folks don't get a choice of whether or not they get stationed in a high-cost area (think Washington, DC) and a 3 year tour with high housing costs plus an incredibly long commute can not only make it impossible to save, it can cause people to dig into previous savings.
My comments are not meant to imply that a cola'd pension is not a very nice thing - it is- but there is a lot more to it than meets the eye.