I think it depend on which method do you use. In my idea, there are several change detection method:
1) post classification comparison
This method firstly classify the images on two dates, and then the classification results are compared. Atmospheric correction is not necessary for the method because classification procedure is not sensitive to atmospheric condition.

2) Change Vector Analysis
This method compare the radiometric value of two images. So, the atmospheric correction is important because the atmospheric condition may be different on the two dates.

3) Methods based on NDVI
NDVI is affected by atmospheric condition, but not very seriously in my idea. I would like to say it is in argue whether atmospheric correction is needed for NDVI comparison. I think it depends on your data.

I wish these answers is helpful for you. And because I am not English native speaker, my expression must has problems. But I wish it can not hinder your understanding