It may have more to do with the timing of the service interval.
If you are doing a radiator flush like every 50K miles for example, the thermostat may be due for a replacement at the second flush interval.
Replacing it won't hurt, regardless, as the part is about $30. I wouldn't replace it unless you are noticing signs of high operating temperatures lately...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car