In Mortal Kombat (aka Mortal Kombat 9, 2011 version) for the PS3 and Xbox 360, you can escape throws fairly easily if you can time it correctly.
To escape a throw, you just need to press front punch or front kick right as they grab you for the throw (X or A on Xbox 360, Square or X on PS3, with default button layouts). If done properly, you will cancel the throw, and you’ll both be pushed away from each other.
You can not hold the block button to perform a throw escape. You can be blocking while the throw starts, but you must let go of block in order to actually escape the throw successfully.