so they're just dvd cases with holes in them?
meh, big deal. Yeah you can argue that there's less "protection" by there being less plastic behind the disc, but consider the fact that really, the disc is suspended in a dvd case, the disc never touches plastic anyhow.
The warping issue, maybe, I could see these cases warping more drastically in extreme heat, but you shouldn't be storing your games in places like that anyhow.
Fragile? I doubt they'll be any more prone to damage or breakage than regular DVD cases, and besides, most users here aren't the type to put their games in situations where damage like that can occur anyhow.
And yes, they're lighter, that's what the holes are for. There's no reason to think they'll warp the artwork unless the case itself warps, and for that, well see above.