Dang, what is the deal with accounts being unfairly blocked from submitting links? And can mods apply this punishment arbitrarily?

Some accounts are allowed to submit links frequently, even a few minutes between submissions, while other accounts are being blocked from submitting and can only do so once every few or 24 hours. "You're posting too fast. Please slow down. Thanks." Is this some type of new punitive action?

It also looks very unfair, when applied to accounts that are clearly not spammers (and maybe submit a few times in a day or week) or appears as a punitive action because of some difference of opinion with a mod.