Well, ctype_digit takes strings, not integers. So don't be surprised if you pass the wrong type to a function and it doesn't work as you expected.
Some of your criticism is valid, but you can't go around talking about how PHP isn't rigorous enough, and then complain tha some functions don't work as you'd like when you give them a wrong argument type.
Your other arguments are more about bad developers as you say it yourself, anyone who actually cares about what he does knows you have to check equality with ===, while the array argument problem is less well known, but actually almost unrelated to PHP: POST or GET is user data that can be any type and should be checked. Only the last of your examples is actually a problem to me.