Is the temp fluctuation causing any problems for you? A 2 degree swing (I'm assuming it's not going significantly under 32F, since it would be forming ice) isn't really a lot, any benefit from getting a tighter margin would probably be outweighed by the added wear from short cycling your compressor. Also remember that your keg is larger than your cup of water, and therefor is going to swing less.

The A419 is a good t-stat, but usually doesn't control temperature significantly better than the factory installed temp control for most refrigeration applications. I actually prefer the A19 with the coil bulb for regular cabinet refrigeration purposes such as a small kegerator.