I doubt they mean single stone, the stats likely refer to total weight, as side stones are so popular now. I haven't been in a jewelry store in years, but I worked for some chains in college and the average person, IME, isn't always interested in quality. Zales.com has some 2.5 CTW rings (that I personally do not care for) for under 4k. And even 1ct solitaires "certified" for that price. They are by no means great stones by many peoples standards, but the average mall jewelry store customer doesn't know much about cut, clarity and color.
I'm totally with you on the insane cost of weddings here though. DH and I ended up having a destination wedding and I was shocked at how much cheaper the food, wine, flowers, cake, and even venue was in Italy vs here.