No, they aren't. Not even close. Just because they have a scratch resistance coating (effictiveness varies on the type of coating used btw, some aren't worth squat) doesn't mean they are scratch proof, particularly when rubbing them against something as rough as cardboard, and even more so if a speck of dust or sand gets between the disc and cardboard. You do know how hard a single grain of sand is right? And, unlike a DVD, a single, minor scratch can render a blu-ray completely worthless due to the way the data is stored.
I swear, I wish people could master basic google before spouting off inaccuracies such as this, plenty of other sites have discussed blu ray scratches before. Even if it doesn't happen to you, there are too many cases of the whole "cardboard packaging scratching blu rays" to ignore. And I'd really expect a CAG to know better... or have you never rented or purchased a used PS3 game before?