I'm curious, in the areas were exclusivity is automatically assumed from the first date, are we talking about the same thing? I think of a date as any time you invite someone out with the potential for romantic involvement either then or in the future. What I mean is that, for example, you meet someone at a party and exchange numbers. Even the first time get together afterwards, say for coffee, that would qualify as a date, as would the times after that when it is not the first, get to know you, moment. In archaic terms, there is a difference between dating, which may or may not be exclusive and "going steady" which mean exclusive.
Yes, even the first time you meet for coffee, I would assume that my date had on other prospects lined up, and wouldn't ask anyone else out until we had decided whether to date again, or not. I would be pretty shocked to discover that I had dated someone twice and they had been to coffee with another partner in between.
I wouldn't even assume that was a date, much less any indication of exclusivity! I went out with DH 3 or 4 times (plus a number of phone calls in between) before I was sure he was interested in more than hanging out as friends. Granted, I am rather clueless in that respect, but even if it had been apparent (even to me) that there was definite possible romantic interest, I wouldn't consider meeting for coffee (heck, even going out for dinner the first time) as anything more than the most basic of getting to know you encounters - finding out if they have reasonable hygiene standards, that you're able to communicate with them, neither of you finds the other completely repulsive, that sort of thing. I can't imagine committing to one person until I've gotten to know them well enough to know I want to spend some real time with them - not just a coffee here or a dinner there or drinks with friends. And that's going to take multiple one-on-one meetings, and probably some chatting via phone and/or online in between, and establishing that we're looking for similar things in a relationship. Sure, sometimes you can meet someone and get that gut feeling and it works out well, but I'm not inclined to hand over heart & soul without a very good idea of what I am getting into.
No-one's handing over heart and soul on their firsts date. You just assume that if someone is showing any kind of interest in you as a potential romantic partner that they have no other prospects for romantic partners on the go at the same time. There's no need for the 'are we exclusive?' conversation, because if you decide to go on another date, and then another, you 'know' that you are, by default.
If you decide after one date or two that you don't mesh, you don't date again, and find someone else.
If I'm serious enough to exclude all others, then yea, I am handing over heart and soul. Or at least access to them. I would not exclude all others unless I thought there was a pretty good shot they were The One.
And I think this is where the confusion begins - I won't consider exclusivity without that, but it seems some folks won't consider that possibility until there is exclusivity.
I think "exclusive" can be used in two different ways.
As my fellow Aussie posters have said, in Australia most people date one person at a time. In that sense, if you go on a first/second date with someone, you're "exclusive" in the sense that you are not dating anyone else. However, you are not yet "exclusive" in the sense that you're a committed couple, calling each other "boyfriend and girlfriend". That second definition of "exclusive" generally comes once you've kissed/had some sort of physical contact.
So, as an example:
Bruce and Sheila go on two dates, There is no kissing or physical contact. Bruce and Sheila still consider themselves "single", however, it's an unspoken convention that neither of them is dating anyone else.
Bruce and Sheila go on a third date and end up snogging on Sheila's doorstep when Bruce drops her home. It's an unspoken convention that they are now a couple, in a relationship.
I think you hit it on the head. I wouldn't call it exclusive unless I was willing to commit, and my partner is too. To me, exclusivity indicates a relatively serious commitment. It seems that for some, it means you're giving Partner 1 a test drive, and won't consider Partner 2 unless Partner 1 doesn't work out. But I won't rule out Partner 2 unless I have a strong indication that a) Partner 2 won't work, and/or b) Partner 1 is The One. Just because Partner 1 is getting a shot, doesn't mean Partner 2 isn't.
It's more like test-driving a car to me - I won't rule out one unless it's ruled itself out, or unless I am ready to buy another. I wouldn't declare exclusivity to one person unless I was sure I didn't want anyone else (either because that one person was That Compatible, or the other available options had ruled themselves out).