ACR X ENCOUNTERED TURB ON APCH BEHIND B-757. POSSIBLE LTSS.

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ACR X ENRTE DSCNT FROM 17000 FT TO 11000 FT. ATC (ZME) ISSUED A SPD OF 190 KTS. THE CLRNC WAS ISSUED WITHOUT CONSIDERATION IF THE FLC WOULD ACCEPT IT; I.E.; ATC EXPECTED THIS PERFORMANCE AND ADHERENCE. OUR ALT AND SPD RESPECTIVELY; WERE 14000 FT DSNDING; 246 KTS. ATC MANUAL 7110.65G PARAGRAPH 5-102 MINIMA 'UNLESS A PLT CONCURS IN THE USE OF A LOWER SPD; USE THE FOLLOWING MINIMA: A) TO ACFT OPERATING BTWN FL280 AND 10000 FT; A SPD NOT LESS THAN 250 KTS OR THE....' DURING AN ILS APCH CONDUCTED IN IMC; WE WERE FOLLOWING A B757. ATC INFORMED US THAT WE WERE '4 MI IN TRAIL OF PRECEDING TFC; MAINTAIN 170 KTS TO THE MARKER...' BECAUSE WE ENCOUNTERED MODERATE CHOP AT 4000 FT; WE QUESTIONED ATC WHAT TYPE OF ACFT WE WERE FOLLOWING ON THE APCH. RESPONSE; ' A B-757 AT 4 MI.' OUR TCASII DISPLAY WAS 3-1/2 - 3-3/4 MI. WE IMMEDIATELY ADJUSTED OUR FLT PATH AND SPD TO CLR OUR POS; ALTHOUGH WE CONTINUED THE APCH AFTER THE TURB SUBSIDED. THE TWR ALONG WITH APCH CTL NEVER ADVISED US OF THE B-757. NEVER ISSUED WAKE TURB ADVISORY OR APPLICATION. WE DID NOT KNOW. REF IS 7110.65G PARAGRAPH 5-70; IE; 5 MI SEPARATION (5- 72(D)(2) AND (F)(2)). RECENTLY; THE FAA ADMINISTRATOR SENT A LETTER TO AIRMEN REGARDING B-757 WAKE TURB AND ATC SPECIFIC HANDLING. IN BOTH CASES NOTED ABOVE ; ZME AND BNA APCH CTL DO NOT DISPLAY PROPER APPLICATION OF THE 7110.65G. HANDBOOK AND THE LETTER TO AIRMEN.