No, you should generally not delete them from your account. The "open" count is based on a blank image that gets displayed when the subscriber opens your email. In some cases, the image does not get display yet they still received your email.
Some reasons why the "open" might not register:
- The subscriber has an email reader that does not display images
- The subscriber receives your email in plain text form
- It is also possible that a given subscriber will open some, but not all, of your emails.