I would never dream of inflicting myself and my husband on our adult kids when it comes to holidays, even though we are more than happy to pay for them.
I had one family holiday with both my parents when I was six, thank goodness it was never repeated! 
We took our kids on educational trips when they were young as we considered it important to do so, but holidays have never been a source of pleasure for me, even though my husband enjoys them.
You didn't go on holiday with your parents after the age of six? Did you really mean that?
I get you aren't keen on holidays, you're not alone there, I know others who feel the same way. Short breaks can be nice though.
Grandparents ARE family...aren't they?! Family holidays normally include grandparents (unless they don't want to go somewhere or are unable). That is the norm in India and in many eastern countries.
Agree sririam, a lot of people holiday with the grands and other extended family here too but it's not unusual for mum, dad and kids to go away on their own or maybe with siblings. Let's face it, there are no hard and fast rules.
My parents and my in laws used to take us & my sister away for a week or maybe more, once we had the kids. My sister in law (husband's sis), and her husband had two children and they were frequently incorporated.
However we did have holidays on our own too. Like this year, a week in Yorkshire which included my dad, a week in North Devon with my sister and bro in law and two of our adult children.
Then husb and I went to America to see our eldest and celebrate his 6Oth. OUr youngest daughter came with.
Last year we had two weeks in N Devon, which was bliss.
Husband's sister and bro-in-law live in West Sussex, in the hospitality industry. We are always welcome there but don't go in peak season. My in laws went just before Christmas and came back on 27th, grandson drove them home & all came to us for supper. We've had some amazing times there, including my parents who really loved them.
So, yes, I think it is quite normal to include grandparents and extended family in holidays but not all the time. It's lovely to get away on your own. Last year in September Chas and I went to Kefalonia in September and it was sheer bliss!
I feel sad that my dad and in laws now feel they don't want to travel far, though I understand it. They will still have 'little' holidays in this country, they will enjoy life for as long as they can.