BE40 INBOUND TO LAS ARE ADVISED BY ARTCC TO EXPECT RWY 19R BUT ARE ISSUED RWY 25L BY THE APCH CTLR.

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FLYING IFR FROM KOUN TO KLAS; WE WERE TOLD BY LOS ANGELES CENTER TO EXPECT RWY 19R FOR APCH AND LNDG. ASSIGNED TO THE LYNSEY RNAV ONE ARR; WE PLANNED FOR THE RWY 19R TRANSITION. APPROX 30 SECS BEFORE THE MIROCK INTXN; LAS VEGAS APCH CTL INSTRUCTS US TO FLY THE RWY 25L TRANSITION. WE DID NOT HAVE ENOUGH TIME TO PROGRAM IN THE NEXT FIX FOR THAT TRANSITION UPON ARRIVING AT MIROCK. WE APPROXIMATED OUR HEADING TO UTARE INTXN. PROMPTLY AFTER ARRIVING AT MIROCK; ATC INFORMED US THAT WE WERE OFF COURSE. WE INFORMED THEM THAT WE WOULD NEED A VECTOR. ALTHOUGH THE ARR PROC DEFAULTS TO THE RWY 25L TRANSITION THE CREW BELIEVES TWO FACTORS CONTRIBUTED TO THE DEVIATION. THESE ARE: 1) PREVIOUS CENTER COM TO EXPECT THE RWY 19R ARR. 2) LAS VEGAS APCH INFORMING US 30 SECS PRIOR TO REACHING THE CRUCIAL FIX. NO EVASIVE ACTION WAS NEEDED; NO TFC CONFLICTS AROSE; AND NO AIRSPACE WAS VIOLATED. A NORMAL APCH TO LND WAS MADE. UPON ARR; LAS VEGAS GND ASKED US TO CALL THE SUPVR. THE SUPVR WAS CONTACTED AND THE CONVERSATION STARTED WITH A GREAT DEAL OF HOSTILITY AND SARCASM FROM HIM. HE ACCUSED THE CREW OF LAUGHING ON FREQ AND THAT 'HE HAD A BIG JOKE FOR US!' I CAN; WITHOUT ANY DOUBT; SAY THAT THERE WAS ABSOLUTELY NO LAUGHING OR INAPPROPRIATE RADIO COM OF ANY SORT. WE WERE CARRYING PASSENGERS AT THE TIME AND OFTEN BACKGROUND NOISE CAN BE HEARD OVER THE RADIO. THAT IS THE ONLY POSSIBLE EXPLANATION I CAN THINK OF. THE SUPVR ALSO INFORMED MYSELF THAT THEY HAVE HAD MANY DEVIATIONS ON THIS RTE AND THAT THEY WERE GETTING TIRED OF IT.