These are just usability guidelines, almost all of which are dealbreakers for me when I visit sites.
For example, when I use my password manager to generate a 64 char password for a new account somewhere, and get an error message saying "Please limit your password to 3 to 20 chars using only letters and numbers," I just have to laugh to myself.
I mean, think about what this tells you about the creators of that site.
I don't want my card details to be saved, and typing in my address and card number take less than a minute anyway. Newsletters almost universally go to spam because I'm not a landowner who has the disposable income to just buy arbitrary things that are advertised to me.
I think generally developers are aware of this, but they're chasing the few that do respond to such tactics.
Just think of the huge number of people have kindles with 1 click buy.
The 'few' indeed.
Most websites aren't special enough to warrant yet another account. Of course they need to keep track of people.
For example, it's interesting that a site within the past couple of minutes to sign into could use a local account, facebook or google... I clicked fb first, they wanted contact info and my full friends list... google, just my email... so I let it in with my google account.
I think it really depends... I wouldn't offer social logins without also having a local option, but it really depends on your audience.
And it also tells Facebook / Google etc what other sites you use, which is none of their business (not that they won't grab that info because of like buttons, analytics, embedded fonts or hosted JS but that's another matter).
A ticketing startup is a good example of a startup which could be used without a dedicated user account. But that's the minority.