<kidding around> Instant 100% upgrade in disk space? Maybe if the disk in question was a 720k floppy disk which the technician punched out the upper left hand corner square. ::snap:: Instant 100% upgrade to 1.44 meg!!!

No really, I can kind of agree with peter on grounds of: Maybe it's significantly cheaper to manufacturer a single physical drive and just limit them different ways to create your product line up. When they want to antiquate the 40gig, they could just stop limiting their, lets say 160 gig, to 40. And when they want to make a 180 gig, they could just research and develop a 320 gig and limit that.

<speculation, don't flame too hard> By only manufacturing these two physical drives, the company could: save on production cost, reduce support and RMA complexity, spend more money on R&D to create their NEXT big-step-up drive, still offer a wide selection of capacities, maybe even get a performance gain from short-stroke heads, AND still sell enough to make this all profitable. ::goes off to start a hard drive fabrication plant::