I will argue that this all still comes down to Apple being a design-led company, rather than an engineering-led one.
Apple doesn't do removable batteries because it undercuts their design philosophy. Apple is all about minimalism and purity in hardware design. In the eyes of Steve Jobs and Jony Ive, perfect products are made by cutting out everything not absolutely required in the design. To them, it's about creating products that are cut down to their absolute most basic form, with nothing standing between the user and the device. The products aren't about having the most features or being the "most useful", but about distilling out the purest mixture of form and function possible.
It's obviously not something everyone agrees upon, but it bears remembering that this is all through the eyes of Apple's design department, not the general population. And while you may disagree, you have to admit that Apple is close to correct. No media device saw the success of the iPod in its heyday, because of the flawless mix of usability and beauty. Up until the iPhone, phones were devices used by phone companies to sell service plans. People talk about the "planned obsolescence" of the iPhone because of the removable battery, but they don't remember the crap phones from decades years ago that fell apart if you sneezed on them. Sure, you could replace the battery, but the battery lasted like six months. Yeah, the phones took removable media, but the internal memory was measured in tens of megabytes, not the gigabytes we have now. Apple's design philosophy, whether or not you agree with it, has totally reshaped the phone and computer industries over the past decade, because it works, and we are better off for it.
So what does this have to do with replaceable media? Simple. Apple believes that it's better to have a high capacity, monolithic phone than one with an extra "feature" that many people don't care about, or even need. Sure, there will be some users who want it, but Apple doesn't care about that. If they listened to what people wanted, we wouldn't have the iPhone, iPad, or anything else like them on the market. No one wanted an iPad when it was announced, until they started using them. For the people that do truly need removable media for whatever reason, Apple really doesn't care about them. It's sort of a niche feature, and Apple has proved time and time again that they don't care about niche features or markets (See: 17" MBP, XServe, Airport, iPod Classic, or other useful products that Apple has either discontinued or left for dead.)
You see the same philosophy in the lack of removable battery. Apple has decided that doing so would sacrifice the integrity and the beauty of the phone were the battery made removable, and I will argue that they are right. Having a solid frame with an internal battery makes the phone more durable than it would be at the same form with a removable battery, and the battery lasts longer too, because it can be built larger within the phone. Why not just make the phone bigger? Because that would compromise the design principles. Again, Apple is trying to make the most pure product possible, in their eyes. Thin, light, yet uncompromising simplicity is the goal here.
That, not a huge feature list, is what Apple believes makes a product good.
It only looks like forced obsolescence to the uninitiated.
