Thanks for all the replies. I was amazed how many people had taken the trouble to answer this one.
One of the comments that resonated in particular was about 'enough'. To an N there is never enough love, and what little there is has to be rationed. For this reason they see the birth of a sibling or a child or grandchild as competition to be fought off.
I think my parents view of money parallels this. My older brother and I are perfectly self sufficient, and have been for years. My parents give me nothing, even though I am not working. Not a penny. My younger brother used to help out, but that stopped two years ago, when he thought he had helped enough. Before that he was very generous, in a spasmodic kind of way. But he did help me. He told me then that he did not expect to be repaid, and I told him that even though he did not expect it, I would repay him, when I sold my house. I was going to do that last year, but delayed in the end because of several factors.
My parents accepted the holidays before, without any problem as far as I am aware. I am not sure why this time they feel differently, unless it is because of the wedding, and they feel they should be contributing more to that. I don't think yb feels that way, but I suppose I can understand them not being able to give him something substantial as a wedding present.
I honestly don't want anything from my parents. But I also don't want to be treated as if what I give to my parents is not important, just because it is not expensive, if that makes any sense. I think this is the part where I have to learn to get over it, yet again. The value of duty and the real kind of love (the kind that tells the truth) is never going to be recognised.
I think my Nmum believes herself to be immortal, so she keeps out of all this talk, and blanks it out. Dad is a bit more rational, and knows he is not immortal, and wants to do the right thing, as far as he can with Nmum around. I don't think it is in our family to be unfair, just as I don't think any of us would actually argue about who gets what. We have seen that with other extended family, and none of us would do that, I believe.
I think the suggestion of a will is a good idea, if I could get them to grasp that particular nettle. I have a CD rom package for writing wills, so it might be worth a try giving that to dad to play with.
Meanwhile, I will settle for getting my reward in heaven. Best way.

I think another part of this is that when I look at my parents I do not see two people either enjoying life or even living. I see two people basically sitting there, waiting for their lives to end. Nmum in the house, dad mostly in the garden.
I would prefer it if they sold their house and went round the world for 3 years and spent every penny, if it meant that they learnt what life actually is all about, and found themselves part of it. Perhaps that is why I am troubled with this. Why sit there and plan what to do with the money once they are dead? They already are dead.
Hope that doesn't sound too unkind.