Partially true.
You can still use the regular (and arguably more stable) mysql extensions with higher versions. I personally build PHP5 against MySQL 5.0a on one of my boxes and it doesn't complain.
One thing you might want to keep in mind though... on the very same pages of the manual (yes, I have already read it, but thanks for quoting it anyway :rolleyes: ), it also states that the MySQLi extension is experimental. Usually when I see words like that, I don't expect stuff to work perfectly.