Thermocouple amplifier - single-ended vs differential?
Thermocouple circuits are just loops of wire, and in industrial situations may be rather long loops of wire.  In this case they are subject to what is called common-mode noise, in particular high-voltage induced AC.

The idea being any induced noise will appear essentially the same on both wires, and the differential amplifier will subtract it out.

Thus differential amplifiers provide a much cleaner signal than a single ended amplifier (with one side of the input tied to ground).  The ability of the differential amplifier to filter out common-mode noise is a parameter called the CMRR (common-mode rejection ratio).

Here is a thermocouple system using a number of Linear Technology parts.  The differential amplifier is the LT2057 (shaded).