Actually, it’s not 
Here’s the rule:
Polls cannot be modified/updated/renamed/changed 5 minutes after their inception.
Pass that time, we only allow staff members to fix a typo (ie. edit the content of an option).
I just pushed a fix that will hopefully improve the copy and make it clearer 
https://github.com/discourse/discourse/commit/c1bb7bc7cc54059073b1dccc83a707936ca16b67