Yes, comfort is the main attraction for a young child. It's not going to be sexual even, heaven forfend, for a randy eleven year old boy if he's been doing it nightly since baby hood. Any more thsn it's sexual for a fully mature, sexually active woman. It is the fact that it can be perceived as sexual which is the difficulty. And I do think that an eleven year old would be highly unusual if they didn't mind or notice that. Likewise the mother.
I suspect that the main thing that brings extended breastfeeders (the children, that is) to the end of their b/feeding habit, is the awareness that it is 'for babies'. A childhood is for growing up in. They are always reaching forwards and even the mother who wishes it wouldn't happen so fast is onto a loser ... But as mothers we are contracted to support their efforts to grow up AND their need to reach 'backwards' into what is familiar.
The extent to which one child or another reaches forward, or back, depends on the child. It is a lucky child who finds him or herself with a mother who entirely supports both the growing up and the hanging on to old habits.
It's a shame that the third voice in the relationship is society's voice, and that it's seldom sympathetic, but then, how else could it be?
Cristina, I can understand your feeling uncomfortable at your son's wanting to 'try' - it is not a habit to him, so he'd be experiencing your body differently from normal. It's the habitual nature of b/feeding that makes it such a huge and vital part of babyhood, and potentially so difficult to separate from childhood.
I suppose a little bit of crossover between babyhood and childhood is no great sin - certainly ought not to be such a huge big deal!