Comparing London and Cologne only make the Cologne events look worse - London has ten times the population and loads of people visit for NYE.
In theory men from countries where women aren't as respected, especially women who dress in clothing that doesn't cover everything, would be more of an assault risk, but I have to say that I've never noticed tons of hassle from the Bengalis in my area, where they are a majority, or noticed anything odd (in body language or comments) about any of my Syrian or ME male students. So this mass attack is extra confusing to me.