Are there different revisions of Arduino Uno SMD?
The only difference with the SMD Uno is the fact you can't remove the chip. There are also 2 extra analog comparators not connected to anything.

The SMD boards are compatible with the thru-hole boards, but they have SMD components, which apparently make them easier to make and cheaper. As I said before, the two extra analog inputs (A7 and A6) are left unconnected on the official boards.

Here is my Uno R3: