I've asked the original question because I clearly saw a regression (or increased security - depending on your point of view) in the way Safari 6 determined WHEN to store passwords. I'm glad to see I'm not the only one with this frustrating issue! 🙂
Being a web developer, I've done tons of authentication portals, and I've never used any sort of "deny saving passwords" feature. (I'm not saying they don't exist, I've seen Microsoft use a few...) Then, suddenly, when Safari 6 comes out, many of MY websites (stored on multiple / different servers, so that I'm pretty sure it's not a server configuration issue) don't save passwords anymore.
I really don't mind that Safari refuses to store them or not, as long as Apple publishes rules to developers on when they will be stored - or not. For example, I've seen examples that, when using Dreamweaver's Spry library on login forms, passwords are not stored. However, there is no clear behaviour that I've been able to pinpoint.
As a sidenote: Firefox easily stores username / passwords on Apple's own Wiki servers (10.7 and 10.8) authentication forms, while Safari, on its own Wiki, won't even prompt you to save it... It does feel that someone dropped the ball somewhere.
I like Safari, and I want to continue using it. Firefox is good too, but also MUCH better in determining when to offer to store passwords. I'd like Safari to be as flexible as Firefox for that. And if not, Apple's feedback on the behavious would be greatly appreciated.