The actual graduation ceremony is often difficult to attend unless you are immediate family. Not only are there restrictions on how many tickets you can obtain, but they are often hours long and mind-numbingly boring. People who get offended about not being invited to the ceremony seem quite ignorant about how these things work.
This. In my experience, graduates are given only so many tickets for the graduation ceremony. My younger DS got 4. And you're right...the ceremonies are pretty tedious!
It's pretty similar in Canada. Of course I'm not going to criticize US traditions but it's just different here.
Overall, HS graduation is treated as an expectation rather than a special accomplishment. With very few exceptions - any student who wants to graduate does so, even if it's within a special program - such as one that accommodates learning disabilities. Generally, gifts are given only from parents and perhaps very close relatives such as grandparents.
Yes, there are ceremonies and parties - but usually parties are given by parents of a graduating senior and include only their kid's friends. There are generally not parties that include adult neighbours, parents' friends, extended family such as great-aunts etc. I am not saying that anyone who did such a party here would be considered "rude", but it would be in raised-eyebrow territory.
But late Dh and I recognised that things were different in the US when we booked a night in Coupeville WA (we needed to catch the ferry the next day). We'd previously seen (on a prior trip) some picturesque B&Bs but found that they were all fully booked even for a Thursday in early June. Even for the nice hotel that we were able to book a few weeks ahead - the manager informed us that it had been the last room available and she seemed to figure that this was perfectly normal at that time of year - "it's graduation weekend!" And yes, while strolling the town (it's pretty small) we saw plenty of license plates from California, Montana, Arizona etc. Naturally not all of these people would have been attending the graduation ceremony, but it would seem to convey that in the US it's very mainstream to drive for a day or two to attend a HS graduation.
So overall, I'd think that this would be a know-your-audience situation. While no announcement or invitation is a gift-summon - if I received a graduation announcement, I would indeed think that a gift was expected.