I agree with the Ziploc comment. That seems to be the best way to go, if you take an e-reader to the beach. I also agree that it's not something I'd leave lying around when I went off somewhere else. Just sounds like a bad idea.
I've seen the same advertisements. The one on the beach is actually the more reasonable commercial. The only thing that I think hurts it a bit is when the woman says she paid more for her sunglasses. Not sure I'd like to say I have anything in common with someone who'd pay $140 for sunglasses.