Thermostats replacement ?

[labii]

I just had the waterpump replaced on my 150 yamaha by my dealer/marina . It had not been done for a couple of seasons . They replaced the thermostats at the same time . I have not done that before and the dealer did it without asking . It is not a big deal if it is something that should be done . I have owned many outbaords in the past and don't remember having them changed before . My question is this a common item that should be replaced as part of a scheduled maintenance process ?