Yes, my boyfriend and I say these things to each other often. Though, admittedly, it probably sounds a bit nauseatingly cute, but we only do it when we're alone together, not when others are around to be nauseated.

It's fun. I think an insecure person wouldn't ask such a question, because they'd be afraid the answer would be "no." We say it because we know the answer is "yes." Though, yeah, we do sometimes answer sarcastically too, because we both have a sarcastic sense of humor. For example, if my boyfriend asks if I love him, I might answer, "Most of the time," or "Nah, I only hang around with you for the sex." But, when I say things like that, it's totally obvious I'm joking. Of course, we also have a thing where if one of us says, "I love you," instead of being cliche and automatically answering "I love you" back, we sometimes answer, "I know." And follow that up with more nauseatingly cute, "How do you know?"
I better stop, I can sense Cyrus turning green around the gills with this.