In thinking about the food on board options it's important not to think of just your own situation on one flight, but other situations:
--like having a very tight transit time, not allowing you to comfortably purchase food
--not wanting to have perishable food unchilled for 8+ hours (the second meal removal on East Coast North American flights)
--having the meal service to break-up the monotony and boredom, especially for kids and other impatient travellers
etc...

For me, an issue is that BA sells itself as a full service airline, so the expectations, and usually price tag are higher.