Also, should you want to change the locale (via a preference or override somehow), in most browsers you can pass it as the first parameter.
I think your view is very much a classic developers view - sure it would be nice to be able to dictate software requirements to businesses but you are probably going to be quite angry as your version of right and someone else's are going to be different.
There are absolutely no usecases where the US date format makes sense. No, having it written in the order you prefer to pronounce it is not an argument. Especially not in the language where you have to learn spelling. It is just what US people are used to.
The thing is, we sort of are! As I mentioned upthread, notation and language are being strongly influenced by increased use of software in every facet of our lives. The way people note numbers, dates, express search terms, etc. are all impacted by what the software accepts and displays by default. We have an opportunity here to push for positive cultural change around international standardization, so let's make good use of it, instead of squandering it by just implementing whatever seems to resemble the local status quo the most.
What developers also suck at, in practice, is data-typing their output properly. If I see 5/2/11 on a US site while using my work laptop, I can't be sure whether it's the US notation written by the author, or date localized by my browser for UK format, which has the day and month reversed. I can't tell if the date is localized or not, or how it was generated.
Just say no to all that complexity, and use ISO 8601 everywhere. My controversial view here is: in this industry, we're still in a privileged position to force the entire world to standardize on the important things, like dates and times. So let's do so, and get everyone on board with an international standard, instead of just unwittingly pushing the USA defaults. We are pushing things, that comes with "software eating the world". So let's push things that make sense.