Hi Attila - for a start, I am not over 50 - in fact quite a way off yet (although I currently feel about 90 ) and I do see what you are saying, but it seems to boil down to one thing ... the expectation that grandparents SHOULD do things in a particular way. These are your (not you specifically) expectations. Peoples lives would be much better if they stopped expecting things to happen in a way that would suit them and just get on with it.
I disagree that there is a 'unwritten assumption' out-there - what is out-there is the assumption on the part of the person who assumes that their parents will be on permenantly on call. I've seen threads on here with people complaining that their parents have booked holidays without matching it to their 'diaries' of what's happening in their lives, or complaining that the grandparents won't look after their grandchildren on a regular basis whilst they go out to work, or even have a social life, or won't give them money to bail them out of debt, etc, etc. I can't understand why there seems to be a general expectation that even once we are adults - we still expect our parents to treat us like their 'little-girls' and bail us out rather than finding our own solutions.
Just like your own mother I made sure that my own children knew that I had been there and done that, I would not be a regular babysitter, I would not be a childminder and they should not make the assumption that I would. That's not meant to sound harsh, but I want to enjoy my grandchildren as exactly that - my grandchildren (that includes being able to see them around my life and commitments, or whatever. When I'm busy, I may not see them much, however, that also doesn't follow that I will see them constantly in my free time). It also means that I do not want to have to take on the responsibilities that I had with my own children. Grandparents should be able to expect the good bits - not all the day-to-day stuff. I too have never attended school plays or fetes, etc, that my grandchildren are involved in - apart from the ones to do with my grandson for who I have parental responsibility. Thats just it - I have parental responsibility and take that seriously, doing whatever a PARENT should do. Lets be honest, such events are pretty boring. My friends with grown up children all back that comment up and admit that we only went, or visited or attended, because our little ones were involved in someway. At the time we would have argued otherwise, but time is a great way of making sure we see things as they really are.
If we start parenthod with no expectations of anyone or assumptions that people will fall into line and behave the way we would like them to, then we can't miss or hanker after things that don't happen, and begin to appreciate the things that do happen.
I also believe (from my work with grandparent groups) that it's not about showing little or no interest in their grandchildren, it's more about not showing the level of interest that our own children automatically assume we should.
There is absolutely nothing wrong with grandparents putting their own selves first, once their own children are grown up.
As for my grandson who lives with us. I absolutely adore him. I have taken on the role of his mother, which makes me very happy, yet also makes me extremely sad ...whilst he has gained substitute parents, he has lost his grandparents. He will never know the exitement of seeing grandma and grandad on visits (or whatever) however frequently or infrequently they might have occured.