[earlz]

A rubberized case wouldn't protect as much. ie, the phone feels more impact from a similar fall except for maybe multi-story drops where most cases don't do anything anyway. Also, this protects the screen from falling onto an uneven surface (think gravel) whereas a rubber case won't help at all, even if it includes one of those annoying plastic screen covers

[vinay427]

Also, cases without bulky screen protectors can't adequately protect curved displays, which are increasingly common nowadays, from falls on non-level surfaces.

[gregmac]

It's almost as if that's a stupid design.

Unfortunately, it's the consumer that pays for that, literally, since they'll have to buy a new phone if it breaks (a win for manufacturer, so long as they buy the same one anyway).