In the example you mentioned, I think that there actually is a difference.

1) You use Firefox, and Microsoft tells you that you should use IE instead. 2) You use Google Search, and Google tells you that you should use Google Search more often.

The first is similar to Google somehow placing notes in Bing Search that Google search is better, the second is similar to Microsoft telling IE users that IE is better than Firefox in [this metric].

I think 1) is ethically more questionable than 2).