yes, User preferences can override this setting. If you do not have the "New" form open setting set to "Default", this field will not be set to "Yes".
To truely set this to "Yes" it is best to do it with workflow on the form opening as each user can have different preference settings (either in the User Tool or central preferences).
Thank you Carl, Manju and Vikram for your help. What i have observed is that the 'Locked' field which is part of the HPD:Helpdesk form (in Work Info tab) with the field name 'Z1D_Editable' has a default value set to No only in this form ( as its default value is Yes in all other forms). Since our customer wants it to be set to Yes, i am planning to change the default value in field properties itself.