[Galaxy S 4 General] BarryH_GEG:
Define "difficult?" What you're describing would have to be an entirely different device. Packaging all the crap (SoC, radio(s), display, speakers, microphones, USB port, control buttons, 3.5mm jack, battery, SD card slot, Wi-Fi, CDMA, BT, and NFC antennas, sensors, etc.) that goes in to a device with the SGS4's dimensions is a feat of engineering. And where all that crap goes so that it fits and doesn't create radio interference or heat dissipation issues is what drives the overall design and materials choices. And kudos to HTC for getting all that crap in to an aluminum unibody. And a “hmm?” for it having the lowest reparability score iFixit’s ever recorded. Electronics packaging and design isn't for the faint of heart.

So to make the SGS4 aluminum they'd have to start over figuring out where all that crap goes based on a new design requirement - aluminum. Would it be "difficult" for a company Samsung's size? No. Would the additional R&D costs and smaller volume sold (I think you'd be surprised how few people would actually pay for aluminum to get the same features) and higher retail price that would drive make it an even remotely profitable proposition? I'd guess not. Out of curiosity, if Samsung plans on selling 10MM plastic SGS4's a month how many aluminum versions do you guys think they'd sell at $150 more? And before you say "whoa, $150?" think about how much more the 64GB versions of Samsung's devices are when the material cost is $10 for 16GB and an additional $20 for 64GB. Part of the huge mark-up is to offset their costs of building and inventorying a device that sells in single digit percentages.

Doing it, even if people were willing to pay extra for it, has an unintended consequence. By Samsung saying "our best" is aluminum it would make it hard to defend everything else in their portfolio being made out of plastic as "best too." It's kind of a slippery slope. Apple’s about to experience the same positioning challenge with the low-cost iPhone Plastic. It’ll be fun watching them say “aluminum’s best” to protect high-end sales while convincing people on a budget that “plastic’s just as good.” As a marketer I don’t envy them.

Samsung experimented with the aluminum G-Tab 7.7 and, for whatever reason, never released another aluminum tablet. Asus’ better spec’d “aluminum” tablets were outsold by Samsung’s plastic ones by 8:1. So I guess Samsung’s not afraid of experimentation but I wouldn't say they're terribly concerned about their competitors using metal either.

And what problem does it solve for Samsung? They’re not deaf and have heard all the *****ing about "plastic" since 2009. Do you think they were taken by surprise that everyone unanimously called the SGS4 "derivitive?" Yet their formula works in spite of the *****ing. If the One suddenly sells 50MM units (over twice HTC's projection) they'd probably take pause in the design of the SGS5. But until something drives them to it I can't see them giving up their love for plastic for a lot of the practical reasons you so eloquently listed.

And this doesn't sound like a person open to suggestions. ;)

Samsung Design America head Dennis Miloseski, speaking at Engadget's Expand conference, played down the importance of materials in handset design, saying that the future of mobile is in creating experiences.

"Actually, the global design process has been raised," Miloseski said. "We're making devices thinner and lighter, screens more beautiful. With Samsung, it's less about that [metal] but more about building a meaningful relationship with technology."

"As these devices become smarter, letting them sense where you are and adjusting to that, it's known that design will improve over time," Miloseski said. "But now, we're thinking about: how do you create a soul for a device."

"The design process doesn't start with a material," he said. "It doesn't start with us saying, 'Okay, we're going to make a device that uses metal.' The design process starts with a story. For a device [like the GS4], which is global and sells around the world, it's a matter of going into many different tastes."​

P.S. - Sorry for the wall'o text but katamari201 raised some interesting points. :)