When a custom display form is generated by SharePoint Designer the attachment will not be exposed if one is present. Please refer to the following link for additional information in regards to custom list forms:
http://office.microsoft.com/en-us/sharepoint-designer-help/create-a-custom-list-form-using-sharepoint-designer-HA010378258.aspx
The out of the box ListFormWebPart does not exhibit this behavior.
http://office.microsoft.com/en-us/sharepoint-designer-help/create-a-custom-list-form-using-sharepoint-designer-HA010378258.aspx
The out of the box ListFormWebPart does not exhibit this behavior.