Not sure if I agree. I find that coming up with good interfaces is often more of a creative challenge than the implementation. API's are worthy of some sort of protection since ease of use is a definite competitive advantage.
Also, you can easily screw your perf with bad interfaces (especially in C++). E.g., not templatizing, requiring extra allocations, type impedance mismatches, vtable bloat, etc. The interface certainly affects how the machine executes your code.
You may be paying for it even if not using it, but you have to account for the environmental savings. But people care less about stuff that's harder to measure.
Yea, looking at this made me realize how uncomfortable my Paperwhite is one-handed. When laying down I usually end up holding it awkwardly with my thumb underneath and my pointer finger straight up the bezel. It's fallen out of my hand too many times to count.
Price aside, this is a worthwhile upgrade simply for the ergonomics.