OP - I think you are getting a raw deal here. It's quite clear from you first post that you were not suggesting the world should forget 9/11 or that the events that happened that day were anything less than shocking and horrific.
Perhaps you've picked the wrong example at the most emotive time.
People can debate all day whether you meant that America has it's eyes closed to the rest of the world or whether you meant Britain cares more for American events than those of any other country. Or something else entirely. But they are jumping the gun and very wrong to accuse you of being jealous of 9/11 or suggesting you mean it shouldn't be remembered outside of America.
I remember reading a book by Bill Bryson, I think it was Notes from a Small Island, in which he writes about the way the British press focuses a great deal on American news while all but ignoring things that happen much closer to home, in France for example, or in countries still linked to us through the monarchy, such as Australia.
This was before 9/11.
In 2009 I was given a book to review and it was made up of news reports of the Obama inauguration, complete with pages and pages of photographs of the story on the front covers of newspapers and magazines from around the world. It's very interesting. I doubt anyone did a similar book for David Cameron (not that he deserves one) even in Britain.
I've tried to think of other terrorist attacks that have happened around the world (Madrid bombings, Tokyo Subway Sarin Gas Attacks) and I couldn't tell you the dates they took place or the amount of years that have gone by.
But I stil think that you are being (not unreasonable) but perhaps forgetful of some of the worldwide events we have remembered recently (such as 25 years from the Chernobyl disaster).
There are some things which we might remark upon more because they happened in a country we are closely affiliated with, and remember for longer, but there are others that are so shocking and terrifying that the whole world will remember for many years to come.
I think 9/11 is one of those things, and would be no matter where it took place, perhaps not because it took place on American soil but because it also took place on television.
The whole world saw the second plane hit the towers and both towers fall, live on their television sets, and they can watch it over and over again via the internet. And once you've seen it, you can't forget it, no matter what country you live in.
And when you think about the memorable moments that have taken place live on television, rather than just reported on afterwards, 9/11 is probably the biggest event ever to be captured as it happened. The whole world shared it so the whole world will remember it now and for many, many years to come.