I left perhaps too much sarcasm and vagueness in my first post. There are two things at play here. First is the combustion unit being quiet which is a good muffler, but also path length tuning, intake design, porting, frame harmonics, and a whole host of other things. Quiet costs both build price, manufacturing quality (macro and micro), and up front engineering.
<--- Engineer with experience designing variable valve timing components.
Separate from this there is efficient and electrically smooth which will be a solid state inverter type drive (of varying quality) vs. other methods of making an AC signal.
I suspect you will find good overlap between the people who are willing to pay for a robust solution in a small light package and those who want quiet smooth electricity.
On the consumer side your DC devices (almost anything with a brick or wall wart) won't care much about how crummy your incoming electricity is. Your AC devices often will care.
