If you only want to collect a email field and not the name field you can remove it from your email subscription forms.
TIP: You can always collect it at a later date using custom fields.
Here is how to do it:
1:Open the survey you want to modify and click on the email subscription widget
2: Click on the "name field" you want to remove
3: Scroll down to the setting area just below,Click the remove this field button.
You are done.
If you scroll back up you will see the name field has now gone.