I think the most basic of amenities are a seat and a working lavoratory, anything else is up for sale, at least in coach.
Check out some of the old airline timetables online that are from the late 60's and early 70's, they listed the prices for each city pair, the fares back then were more expensive than they are now and that was in those years dollars, that is why the airlines could afford to compete on service. Flash forward 30 years and most consumers buy strictly on price, alot say they would pay extra for better service but when push comes to shove price wins out. Remember our More Room Throughout Coach, everybody loved it but the airline found out if another airline was even $5 cheaper they would book the competitor, it went away. Same thing with pillows and blankets, there is a cost associated with keeping them onboard.
Airline travel is not a service industry anymore, it is a transportation industry, the marketing department may try to blow sunshine up your backside but when all we do is sell beverages and meals. I can see selling pillows and blankets onboard in the very near future as a few airlines already do, in fact when I travel I carry a travel pillow and a space blanket, I've worked for an airline long enough that I would never use or let my family use an airline pillow or blanket, they are just foul.
MikeBOS