USPS has increased its shipping prices quite a bit in the last several years, enough that I can (unfortunately) easily see it costing $9.99 or even more to send a box set of DVDs. Try checking the USPS shipping calculator, you might be surprised at the results.
You're generally right but DVDs (and books and CDs) can go media mail and that's very cheap. Like $3 for 3 pounds.
I was selling off some old PC Magazines and Bytes from when I was a teenager and was surprised that magazines aren't supposed to be shipped via media mail since they've got advertisements in them.
