in reply to Re^2: regex to rename last _ with ,
in thread regex to rename last _ with ,

A couple of reasons. First, I can never remember the exact syntax of the look-around assertions, so I have to perldoc perlre each time I use one. This makes it advanced in my mind. I guess this is highly subjective, so your point is taken.

Second, the more features are used in a regular expression, the more there is to translate when you want to use it in another tool. Doing without look-ahead brings the RE to a lower common denominator, so to speak.