BECAUSE OF INADEQUATE SEPARATION; MD80 INTO ATL ENCOUNTERED WAKE TURB AT 100 FT. EXECUTED A GAR.

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ATL APCH TURNED US ONTO A 15 MI FINAL ABOUT 2 1/4 MI BEHIND ANOTHER MD88; TOLD US TO SLOW TO 150 KIAS; AND CLRED US FOR THE VISUAL APCH. WE HAD THE PRECEDING ACFT IN SIGHT AND THOUGHT THAT SINCE WE WERE SLOWED TO 150 KIAS THE SPACING WOULD IMPROVE. 2 MI BEFORE THE OM; WE WERE WITHIN 2 MI AND CLOSING. WE EXPRESSED OUR CONCERN TO APCH CTL ABOUT THE SPACING AND HE TOLD US IT WAS FINE AND HANDED US OFF TO TWR. AT THE OM WE COULD SEE ACFT ON THE PARALLEL RWY; SO LNDG ON THAT RWY WAS NOT AN OPTION. WE CONSIDERED ASKING FOR AN S-TURN BUT WE COULD SEE THE ACFT BEHIND US WAS WITHIN 2 1/2 MI ON THE TCASII. WE TOLD THE TWR THE SPACING WAS TOO CLOSE AND HE TOLD US TO EXPECT LNDG CLRNC ON SHORT FINAL. WE WERE 600 FT AGL WHEN THE ACFT IN FRONT OF US TOUCHED DOWN. AS WE CAME OVER THE APCH LIGHTS AT 100 FT; THE RWY WAS CLR; BUT WE HIT WAKE TURB. THE TURB REQUIRED FULL L AILERON TO KEEP THE WINGS LEVEL. I IMMEDIATELY INITIATED A GAR. ATL APCH ROUTINELY GIVES US 2 1/2 MI OR LESS SPACING ON FINAL; ASSIGNS US A SPD AND HOPES IT WORKS OUT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT HE HAD TALKED TO HIS COMPANY; PLT GROUP; AND THE ATL TWR. NO ONE WAS WILLING TO TAKE ON THE PROB. HE WAS TOLD THAT INSTEAD OF SPACING OF 2 1/2 MI; ATL WAS GOING TO GO TO 2 MI SEPARATION. HE WAS TOLD A FEW MISSED APCHS WERE ACCEPTABLE.