You’re lazy and don’t want to type more characters than necessary, so you stick to 8 characters and replace the c with a 7: "qur7oehx". The site accepts the password.
The puzzler: Is the second version “safer” than the first version? Or, put differently: Are there more 8 character passwords with exactly 1 digit, than there are 8 character passwords with only letters?
being forced to ‘downgrade’ a letter to a digit must surely be bad.
We see that 267×10×8 is greater than 268, so replacing a character with a digit actually helps. What “saves” us here, intuitively, is the fact that the digit has many possible positions.
10×[number of digit positions] > [number of letters].
Even with just 2 characters we’re better off “downgrading” one of them from a letter to a digit.
If we on the other hand consider upper case letters as well, i.e. 52 alternatives, we need more than ⌊52/10⌋ = 5 characters for the downgrade to make sense.
Conclusion: The tongue in cheek security analysis here is, as long as you have a reasonable long password, it’s an improvement to replace a letter with a digit.