No big thing, the T stands for "Touring" (= station wagon).
Before Mercedes adopted the new nomenclature, the wagons were known as 200T/200TE/230TE/300TE/200TD/250TD/300TD in the W124 series, which by the way, to be more precise, in this series the wagon chassis series is internally known as S124 (no relation to the S class).
In the final two years of the S124 production, the series were renamed E200/E220/E280/E320/E250 (diesel)/E300 (diesel)/E300 (turbodiesel). Hence, people added the "T" at the end (ex. E320T) to clarify they were talking about the wagon.
Mercedes-Benz, except for the well known Turbo Diesels is not very fond of turbos on gasoline engines. They preffer the Kompressor units (like the SLK230). I actually cannot recall a single M-B high production turbo gasoline engine in the last four decades.