hook_validate and set_form_value inconsistency

Also applies to D7.

The problem:

From hook_validate documentation:

Changes made to the $node object within a hook_validate() function will have no effect. The preferred method to change a node's content is to use or hook_nodeapi($op='submit') instead. If it is really necessary to change the node at the validate stage, you can use function form_set_value().

I want to call form_set_value from within hook_validate as per documentation. However, hook_validate receives two arguments $node and $form while form_set_value requires three arguments $node, $form, AND $form_state to do the job. In other words calling form_set_value from within hook_validate is impossible since you do not have the form_state in that hook.

I have a specific requirement that I need to set the title of a node if and only if some other values validate.