InputFilter/BaseInputFilter : Data formatting and validation

Hello,

I was wondering why during form validation process, the data passed to validators as $context are raw values ?
$validator->isValid($value, $context);

$value is correctly filtered.
$context is just raw data, no filter applied.

I don't understand the logic behind this.. and I have to "re-filter" the $context vars when I want to use them (code redundancy).