i am not certain about this and it definitely wouldn't apply to many plugins such as some of the Waves plugs, but isn't the fact that Logic uses 32 bit floating point processing, make internal clipping non uniform. ie Not all signal paths work the same way.
TDM is 48bit fixed AFAIK, making this sort of feature more pertinent.
As I mentioned, i am not totally sure about this, as I do have plugs that clip and the behaviour of most is dependent on level.
I think a Plugin Clipping Indicator is a priority feature to add to Logic because you cannot tell clipping when you add lots of clips, whereas if they go red or flash, they are bought to your attention immediately.
I think the Logic developers could go one more step than just adding Plugin Clipping Indicator(s) and that is to have add VDU meter where the green EQ indicator is (just above channel inserts) and as you select (touch) each insert it VDU meter shows whats happening in that plug in.
SOLUTION TO NO PLUG IN INDICATOR
Since Logic does not have a VDU meter plug in I use Waves Puigtec EQ-1A VDU meter and I try to keep each plugin about 3db below zero and the channels sound clearer now. Previously I never checked if there was any clipping between plug ins and the tracks sounded harsh. Note: You can use any plug in that has a VDU Meter.