Should every table have a single-field surrogate/artificial primary key?

I understand one benefit of surrogate/artificial keys in general - they do not change and that can be very convenient. This is true whether they are single or multiple field - as long as they are 'artificial'. However, it sometimes seems to be a matter of policy to have an auto-incrementing integer field as the primary key of each table. Is this always the best idea to have such a **single-field** key and why (or why not)? To be clear, this question is not about artificial vs natural - but about whether all artificial keys should be **single-field**