I think that people often avoid this for two reasons: they don't want to give competitors free advertising, and they don't want to risk people thinking "if this new thing is like this old thing, I'll just stick with the tried-and-true old thing".
IANAL, but in the US, I am not aware of a legal downside as long as you're careful about trademarks. You can use other people's trademarks in ad copy, for instance, as long as you don't do so in a way that could cause consumer confusion (people thinking that the company whose trademark you used is in some way connected with your product.)