Definitely something I didn't think of, but here's my two counter arguements:
1.) I would say that I knew virtually everytime an enemy in my pk range gained a rank in hero pk range

2.) If I'm hunting someone pre-hero the FIRST place I always looked was ranking spots

So, I don't think a gecho announcing someone just heroed gives away that much in the way of valuable of information and besides it's just cool.

I thought it would be even cooler if the imm's could code it if you got a special gecho for your first ever hero (a bit inaccurate since it would likely be by ip address) but thought against it since then you're announcing "I'm kinda new at these ranks, please come kill me" to everybody who hadn't already figured it out.