[Nacraile]

Ah, yes, it is definitely reasonable to draw that conclusion based on people's disinclination to spend 100% the fare for a 10% larger, somewhat less uncomfortable seat, and/or 1000% the fare for 50% more space and an actually comfortable seat.

[leesalminen]

You seem to have left out Premium Economy class that’s available on many (most?) airlines. Personally, I tend to opt for that fare class as I find the seat more tolerable at a reasonable price point.

[throwaway3563]

Premium economy is still usually at least 2x the economy ticket price; on a long haul that will cost many hundreds to up to thousands extra.

What you’re probably thinking of is the US airline specific “comfort/extra/plus” add-on that is priced 10%-20% extra. There is a few more inches legroom but the seats are the same small economy seats.