A320 FLT CREW IS QUERIED BY ATC AS TO THE REASON FOR SLOW EXIT FROM RWY 19R AT IAD; REQUIRING ACFT TO GAR.

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DURING ROLLOUT; TWR ASKED US TO EXIT AT Y7 AND CONTACT GND. CAPT RESPONDED WITH WE WILL TRY OUR BEST. AROUND 30 KTS; XFER OF CTL WAS PERFORMED AND CAPT SLOWED TO 10 KTS TO MAKE TURN BECAUSE THE TURN TO THE HIGH-SPD WAS TOO SHARP. GND WAS CONTACTED AND TOLD US TO HOLD SHORT OF TXWY Z AND CONTACT RAMP. WE COMPLIED. DURING TAXI IN WITH RAMP; THEY TOLD US THAT GND WAS WONDERING WHY WE TOOK SO LONG ON THE RWY. THEY NEVER SAID A WORD TO US WHEN WE TALKED TO THEM. THE CAPT CALLED THE TWR AND THEY TOLD US THAT A PLANE HAD TO GO AROUND BECAUSE WE TOOK TOO LONG. WE TOOK NO LONGER THAN 3-5 SECONDS LONGER THAN USUAL BECAUSE OF THE SHARP TURN. TWR TOLD THE CAPT THAT THE HIGH-SPD IS A 75 KT HIGH-SPD AND SHOULD BE USED AS SUCH. THE CAPT EXPLAINED THAT OUR OPS REQUIRES US TO SLOW TO 10 KTS FOR A 90 DEG TURN. THE SUPVR SAID THERE WAS NO PROB JUST WAS WONDERING IF WE HAD A PROB. IF THE GAR WAS INITIATED BECAUSE OF AN EXTRA FEW SECONDS; THEN SEPARATION WAS NOT WHAT IT SHOULD HAVE BEEN. THIS ALSO COULD BE SOLVED BY NOT LNDG WITH TAILWINDS. THE WIND WAS 010 DEGS AT 8 KTS. I KNOW THERE IS A GOOD NEIGHBOR POLICY; BUT PUTTING ACFT IN SITUATIONS WHERE THEY ARE FORCED TO LAND WITH EXTRA GND SPD AND LONGER ROLLOUTS IS GOING TO CREATE PROBS. SUPPLEMENTAL INFO FROM ACN 783852: NEW COPLT WITH LESS THAN 50 HRS MAKES LNDG ON RWY 19R WITH 5 KTS OF TAILWIND. LNDG NORMAL AND TURNOFF AT T-7 WAS MADE. BRIEF FOR TRANSITION TO THE CAPT WAS SIMPLE; BELOW 60 KTS WITH ACFT STEADY WITH NO SIDE LOADS IN TURNS. AT 40 KTS ABEAM T-9; A 90 DEG TURN WAS STARTED WHICH REQUIRED A MAX 10 KTS GND SPD PER OPS SPEC. GND CTL DID NOT ADVISE ANY ACFT WAS BEHIND US BUT ASKED WE CALL. THEY WANTED TO KNOW WHY THE TURNOFF WAS SLOW. I EXPLAINED THIS TO THE CTLR WHO WAS DETERMINED TO GET ME TO EXIT AT HIGHER SPDS IN THE FUTURE; TELLING ME T-7 WAS A 65 KT HIGH-SPD. SIMPLY DISAPPOINTED THAT THEY WOULD PUSH UNSAFE PRACTICES WHEN THE PIC MUST MAKE EXIT DECISIONS BASED ON ALL THE CONDITIONS. WE NEVER STOPPED THE ACFT ON THE RWY OR TXWY. WE EXITED THE RWY INITIALLY AT 10 KTS THEN 15 KTS APCHING THE NEXT TXWY Z. WE WERE TOLD WE FORCED A COMMUTER TO GAR BUT WAS NEVER ADVISED OF ANY TIME ISSUES ON LNDG.