RPTR UNCOMFORTABLE WITH VISUAL RESPONSIBILITY CHANGES BTWN 3 ACFT ON PARALLEL APCH TO RWY 28L AND RWY 28R AT SFO. RPTR X ACFT WAS TOLD TO SLOW TO 150 KTS AS HE WAS FOLLOWING Y ACFT AND TO ALLOW Z ACFT TO 'CATCH UP' ALONGSIDE; HOWEVER Z ACFT PASSED X WHICH Z WAS NOT SUPPOSED TO DO.

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ACR FLT X HVY WAS INBOUND FROM CEDES INTXN ON A HDG TO INTERCEPT THE SFO VOR 095 DEG RADIAL FOR THE QUIET BRIDGE VISUAL TO RWY 28R. TFC WAS RPTED AS AN ACR FLT Y HVY AT 12 O'CLOCK. THE CREW RPTED THE TFC IN SIGHT. APCH THEN GAVE A HDG OF 230 DEGS FOR SEPARATION. ON THIS HDG; FLT X CROSSED THE CTRLINE OF BOTH RWY 28R AND RWY 28L. TFC WAS OBSERVED AT 12 O'CLOCK; AND A TCASII 'TA' WAS RECEIVED. THE TFC FLASHED HIS LNDG LIGHTS AS FLT X WAS CLRED FOR THE QUIET BRIDGE VISUAL TO RWY 28R. THE OTHER ACFT; ACR FLT Z (B-737) ASKED ABOUT THE TFC; AND WERE TOLD TO 'RPT THE 757 IN SIGHT.' THE 737 DID SO; AND WAS CLRED FOR THE TIP TOE TO RWY 28L. THE 737 WAS GIVEN A SPD OF 180 KTS AND THE 757 WAS TOLD TO SLOW TO 150 KTS TO ALLOW THE 737 TO 'CATCH UP.' WHEN THE 737 WAS 1 MI IN TRAIL AND AT THE SAME ALT; I LOOKED ABACK AND VISUALLY ACQUIRED HIM. THE CTLR ASKED ACR X IF HE HAD THE 737 IN SIGHT; AND HE REPLIED THAT HE DID. AT THE TIME; I WAS WONDERING WHY THE 737 WOULD REMAIN IN THIS HAZARDOUS POS BECAUSE OF WAKE VORTICES (WIND WAS 300 DEGS AT 20 KTS) AT THAT TIME; ATC TOLD ACR X TO MAINTAIN VISUAL SEPARATION FROM THE 737; AS THE 737 PASSED US WITH A 20-30 KT SPD ADVANTAGE. I CONTACTED THE 737 CREW AND THEY TOLD ME THAT THEY UNDERSTOOD THE 'CATCH-UP' TO MEAN 'PASS.' THEY WERE GOING TO PASS; REGARDLESS; TO AVOID THE 757 WAKE. WHILE THE ONUS WAS ON THEM TO MAINTAIN VISUAL AND WAKE SEPARATION; IT APPEARS THAT THIS RESPONSIBILITY WAS TRANSFERRED TO THE 757; WHEN THE OVERTAKE WAS OBVIOUS. WHO'S GOT THE LEAD? WHO GETS VIOLATED FOR LOSING SIGHT/PASSING? VISUALS AT SFO ARE AN AIRSHOW.