I think it is more the mentality of the people... in general, the UK and Australian outlooks are more along the lines of no sacred cows... well, it used to be! Definitely it was more acceptable to poke fun at ourselves (something that I believe shows a strength of nationality and self to be able to do). Likewise, we (I) would poke fun at others if I felt them to be strong enough to handle it, but we wouldn't do it against the weaker... However, this is only one person's perspective!
So, I guess strength through putting your self down (as you have to be strong enough to be able to do that)... but putting others down is not so acceptable, there is no strength in that.
Nothing wrong with putting yourself in jest - or to point out your weaknesses, but when children constantly hear how Europe is doing things so much better than England, it eventually seeps into their being. I heard far more people complain about England and how they'd be better off almost anywhere than I heard of people being proud to be British. Maybe it's just that understating habit that the Brits have (and probably the Aussies by extension) - some Americans have it too, but to a lesser degree.
I suspect it's more related to being more subdued by nature (the Brits) combined with the fact it was generally the more outgoing types who would have emigrated to the Colonies first. Obviously, the situation with Australia was a little different, so it throws out the logic about whether they were more outgoing or not.
The reason I say this is because of my observations regarding cheering...
In the UK, cheering for someone is considered to be a very American thing. Whereas in the US it's very normal - and possibly rude to not cheer.
(BTW, on a totally different note, when I got back to the US, having just spent a year in South Wales, I realized very suddenly that you Aussies have Welsh vowels! I was watching H2O with my girls when I had that revelation.)
It must be a different mindset, I feel pride in my country (mostly), but I'm quite happy to make fun at it! I think that tends to be the same for most of our people. The kids grow up with that same internal and contained pride...
... And with that cheering example, I guess that is at the heart of the difference? I would find it weird to cheer for something that you didn't find good! But cheering, just because it would be rude not to, and because everyone around was cheering... Strikes me as strange! So it is with the overt displays of patriotism!
Ha ha, Australia and Wales! Who would have thought! Although, it is interesting to see how the Australian accent has changed dramatically since WW2. It used to be more 'british'!
It's not that we're cheering for something we don't find good - It's not that we feel forced to. It's just that we wear our heart on our sleeves a little more. There isn't this cultural expectation to be "reserved" and to keep the "stiff upper lip" or to understate everything the way the Brits do. I know they still do this because I learned to do it myself when I lived there.
I guess one of the biggest differences between Europe and the USA is that we made our country - rather than inherit it. Although it wasn't my immediate ancestors who fought - even for the west, I can still tell you who it was in my lineage who helped establish this country. (I am the fifth generation of my line born in the state of Oregon - though none of my children, nor the cousins who shared that part of my lineage, were.)
As we get further and further away from our founders, US patriotism may change within the next 100 years, who knows?
When I looked into Welsh emigration to Australia, it turned out to be a very big thing - probably the greatest single influence other than the original forced settlers. Hence, even, "New South Wales"...