It is the "ticket" which is refunded. The reservation is simply cancelled. The ticket includes taxes and carrier surcharges (I do not know of any carrier which imposes fuel surcharges or has done so for at least 5 years).

All three legacies. UA, DL, and AA, have cancellation policies which exceed the minimum required by DOT, both in terms of the 24 hours (AA, for example, runs through the end of the next day) and what fees will be refunded.