No. When you disable comments, they are *disabled*. Really. It doesn't just remove the form, it stops accepting comments for that post. Form or not, it will not take comments, period.
- Disabling comments globally doesn't change the settings on your old posts. Comments are enabled/disabled on a per post basis, and turning off "Allow people to post comments on the article" only turns it off for new posts, not for old posts.
- Trackbacks and pingbacks are not comments and they too can be enabled/disabled on a per post basis. So even if you turn off comments for a post, trackbacks and pingbacks can still get through unless you turn those off as well.
Go to the Edit Post page for any given post. There's a setting on the right to Allow Comments and Allow Pings. You have to turn both of those off to disallow comments/pingbacks for that post. Changing the global settings in Options->Discussion doesn't change all those settings on your posts. Those only apply to new posts and it says so on the page itself.