If Kerry had been enlisted, you might be right that he would have been discharged in 1972. On other threads discussing Kerry's discharge, freepers who were officers have repeatedly stated that an officer's obligation only terminates if the branch decides to end it or the officer resigns his commission.
I was a Naval officer and retired with 20 years of active and Reserve service.
The term "obligated service" refers to the service time you owe as a result of your contract.
Kerry's contract obligated him to three years of active duty after his commissioning date (16 December 1966), a period in the Ready Reserve that, when added to his active duty service would total five years and additional time in the Standby Reserve until the 6th anniversary of his commissioning.
His "obligated service" therefore ended on 16 December 1966.
It is true, however, that service may be extended beyond obligated service time. This applies to enlisted as well as officers in "Stop-Loss" situations and if UCMJ charges are pending.
Kerry's obligated service ended on 16 December 1972. If he did not get his Honorable Discharge it could be because:
1. Out of purely patriotic reasons, Kerry never resigned his commission in order to be available for future military service in case of national emergency .....(Highly unlikely)
2. Kerry received a less than honorable discharge that was later upgraded to honorable in 1978......(Very plausible)
3. Kerry was involuntarily extended in order to investigate charges prosecutable under the UCMJ. Reservists on Inactive status may be involuntarily detained in the service and even recalled to active duty for UCMJ offenses committed previously while on active duty. Kerry confessed to "war crimes" he allegedly committed in Vietnam while on active duty. Our sea-lawyer may have out-smarted himself.