And here it is: http://en.wikipedia.org/wiki/Wikipedia:Deletion_process
"Non-administrators closing discussions"
According to this, non-admins can close keep results, but shouldn't close delete results. They can even close high disputed keep results, but they are discouraged from doing so if they "are not familiar with deletion policy or the workings of deletion discussions".
The rationale for saying that non-admins shouldn't close delete results is that "they lack the technical ability to delete pages". But that ignores the fact that the vast majority of the work of deletion is deciding what to do, not in hitting the delete button.
I'm not sure that page accurately reflects how things actually are. Policy is determined more by what actually happens than by what is written down.