Keep in mind that Google's margins are extremely thin on the N4, if they exist at all. Some analysts speculate it's negative, and that's prior to the costs of RMAs, etc. Keeping the cost down is about keeping the price down to get people into the OS and ecosystem. Obviously more choices are a good thing, but will there be enough adoption of each choice to justify each level of choice? Hopefully their decisions are based on some market research or analysis of S3 sales, etc.
Some of the lines of thought in the market seem to be very contrary to how it appears that Google solves problems. For example, on storage they looked at the problem of having multiple file systems on multiple partitions, etc. and said, "lets just make that all one giant block of storage". People complained saying, "that's not enough storage", and so they said, "okay, here's unlimited access to all your photos, music, movies, books, documents, e-mail, etc.... all for free, now you don't have to have it all on your device". Clearly there are people that do not like that as a solution because it doesn't work for them the way that they use their devices. Two solutions, presented many multitudes of times: 1. Get a device that works the way you want to use it 2. Change how you use it to fit the device you bought.
Another example is batteries. People said, "I don't want to be tied to the charger all day and my battery doesn't last long enough. Batteries must be removable!" But in Google's mind, your battery shouldn't be dying in a day. Swapable isn't the solution, that's still a battery that doesn't do it's job. They instead intend to have batteries that last days. Again, obviously if you're the person who spends many days at a time away from electricity, but still need to have your screen, music, gps and LTE on non-stop, that's probably not going to help. But for the vast majority of people, if you give them a battery that's still at 65% at the end of the day, my guess is the urge to swap it out decreases.
Of course, I'm speculating based on their words and actions instead of looking at it through the lens of what I want them to do.