the empeg is the only car stereo I ever saw that did the right thing with the antenna

Many newer aftermarket HUs come with 2 wires (which is what the empeg w/ tuner has): one that is remote turn on and is "active" all the time the HU is on and one that is power antenna and is "active" only while the HU is in "tuner mode", suitable for a motor antenna.
Lots of questions on car audio boards about why the amp only turns on while they listen to the radio but not while listening to CDs...

Now with RDS you might still want to run up the aerial (or give juice to an antenna amplifier - integrated into the antenna mount both on my VW Polo and new Pug 206) all the time, in order to get better reception for the tuner as it scans for, for instance, traffic announcements...