doris I don't think you need to express for your 17 month old! I stopped pumping for DD1 when she was 13 months and DD2 when she was about 18 months. I only did it at all because I returned to work when they were 6 months old, and neither of them ate huge amounts of solids so both were still very boob-dependant for food.
As for the misconceptions surrounding how breastfeeding children (as opposed to babies or toddlers) behave, well, my DD1 is now 6½, and would happily nurse 4 or 5 times a day, she just loves breastfeeding, she loves the milk, she loves the cuddling and she loves the act of suckling, she just loves all of it. However, she doesn't dash out of school and rip my top off in her hurry to get to my boobs, in fact, she only really feeds first thing in the morning, when she's snuggling in our bed before we all get up. She knows that she's "a bit old" to be doing it now, so she doesn't often try to ask for it except in bed, first thing. She stopped the bedtime feed over a year ago, and will happily go and sleep over at my folks house, has been on an over-night trip with her school and is unconcerned that I am going to be away for three nights in a couple of weeks.
As for the immune "benefits" of breastfeeding, well, she picked up every bug going as a baby when she was in nursery, but was never really seriously poorly, and now is practically bullet-proof. DD2 currently has a nasty cold, DD1 has only got a slightly bunged up nose. The difference in her immune development was not really noticeable when she was tiny, but now that she's school age it's fairly clear to me that her immune system is fantastic, and I think this is down to her natural term breastfeeding.
And clingy? Clingy?? She is confident, independent, secure, healthy, cuddly, loving and affectionate. I don't think I know many other 6 year olds who still love to curl up on their mum/dad's laps and just cuddle for the sake of cuddling.
So many misconceptions surround Natural Term Breastfeeding, and articles like this one in the Daily Mail only serve to cement these misconceptions into the collective mind of our breastfeeding-unfriendly child-training culture.
It's quite sad really.