A B767-300 FLT FAILS TO MAKE A XING RESTR WHEN THE CREW FAILS TO NOTE THE FMS WAS NOT STARTING THE PROGRAMMED DSCNT AS EXPECTED NEAR STW; PA.

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ON FLT FROM LAX TO JFK; WE WERE CRUISING AT FL370. WE WERE ASSIGNED TO CROSS HARTY INTXN ON THE LENDY 4 ARR TO JFK AT FL230. THE ACFT WAS ON AUTOPLT AND IN VNAV. THE EXPECTED CLRNC ALTS WERE PREVIOUSLY PROGRAMMED INTO THE FMC. UPON RECEIVING THE XING RESTR AT HARTY; THE CAPT ENTERED FL230 IN THE FMC CRUISE PAGE AND EXECUTED THE INSTRUCTION. THE MCP ALT WAS SET TO FL230. I NOTIFIED CTR WE WERE LEAVING FL370 TO FL230. AT THIS TIME I RESUMED MY PNF DUTIES OF UPDATING THE ATIS AND MAKING A FINAL PA TO THE PAX. WHEN I FINISHED; I NOTED THE ACFT WAS STILL AT FL370 AND ONLY 10 MI OR SO TO HARTY. I NOTIFIED THE CAPT; WHO STARTED AN IMMEDIATE DSCNT IN FLT LEVEL CHANGE MODE. I THEN NOTIFIED ATC THAT WE WOULD NOT MAKE THE XING RESTR AT HARTY; AS WE DID HAVE ABOUT AN 80 KT TAILWIND AT THE TIME. WE CROSSED HARTY SOME 1500-2000 FT HIGH. TO MY KNOWLEDGE; NO LOSS OF SEPARATION OCCURRED. THE POINT OF THIS RPT IS THAT THE AUTOMATION IN MODERN AIRLINERS IS GREAT; AND IN MY EXPERIENCE WORKS CORRECTLY 99.9% OF THE TIME. THIS SUCCESS RATE LULLS US INTO COMPLACENCY; BELIEVING THE SYS WILL ALWAYS DO WHAT WE HAVE PROGRAMMED IT TO DO. WHEN USING THE AUTOMATION; HOWEVER; WE SHOULD BE EXTRA VIGILANT TO ENSURE THE AUTOMATION DOES DO WHAT WE WANT IT TO DO! I STILL DON'T KNOW WHY THE ACFT REMAINED AT FL370 WHEN THE NEW CRUISE ALT WAS SET TO FL230. THE FAILURE HERE; HOWEVER; WAS THAT WE FAILED TO NOTICE IMMEDIATELY THAT THE SYS WAS NOT DOING WHAT WE WANTED IT TO DO.