[Moto X General] Johmama:
First, I'm not 100% sure that OEMs have the ability to save hard-bricks. Hard-bricks are the bootloader being corrupt. The bootloader, being the first thing to even load into memory, from which everything else gets loaded into memory, is vital to the bootstrapping process. Think of it like your BIOS on your computer. If you BIOS goes corrupt, you basically either replace the BIOS chip, Mobo, or in super-rare cases, find someone somewhere with the tools, expertise, and ability to flash that specific BIOS to that specific chip even though it's corrupt. I suppose it's possible that the OEMs have those tools to do it. I'm not saying that do, but I'll give you that it's possible. Even if they do, it probably wouldn't be worth the time and effort though.

Second, unlocking the bootloader isn't just giving the ability to flash to the recovery partition, or even to the /system/ partition. It's removing the entire signature check which checks if the package you are trying to flash has a unique signature that comes from the OEM. Unlocking the bootloader basically opens every single command up for anyone besides the OEM to use. It really is as serious as they warn about in the screen asking if you're sure. Now, since communities like XDA exist where you can basically get walked through how to do most anything, and where 1-click toolkits to do very very dangerous stuff exist, it's fairly safe to have your bootloader unlocked. But as an electronics manufacturer, you need to assume the user won't take advantage of tools like XDA. I'm a software engineer and one of the fundamental rules of thumb is "if the user can break it, they will".

Third, you said:

I think you'd be surprised. Have you ever tried to get anything replaced under warranty, then telling the customer support you installed Linux on your box? I mean, you may or may not actually get your warranty honored, and if you do, it will be after a few hours on the phone, getting bounced around, escalated, redirected, on hold, checking with this other guy, etc. before they finally figure it's eligible. We're of course talking about pre-built PCs, to make this analogy fit.

Look, I mean no disrespect or negativity toward you. I'm simply saying that it's pretty much industry standard to void warranties when unlocking the bootloader in any electronics, and as bad as this next part sounds, it's for good reason. If you start preserving warranties through bootloader unlocking on more widely-used or mainstream electronics, then more and more people who shouldn't be tinkering will. Your brick rate, and thus number of replacement units sent out, will go up, and the prices of your electronics will go up to make up for loss. It's good to have warranties preserved through the bootloader unlocking process on niche "developer edition" units because it covers that small percentage of users who want that option, but still bars people who wouldn't mind having that perk, but aren't willing to make the sacrifices necessary to have it. This ultimately makes it so the people who got the "developer edition" of your phone most likely enthusiasts or developers, who know what they're doing, and their brick-rate is probably pretty low.