So I did not reference slicks. I mentioned street legal radials, which are a bit different.
Slicks:
http://www.streettunedmotorsports.com/parts/b/m&h_racemaster_drag_slick.jpg
Radials:
http://i232.photobucket.com/albums/ee301/deanscheidt/255-60-15DragRadials_zps8d2a729f.jpg
They still have tread and are driveable on wet surfaces just like a regular tire. Your example of the ET Street is damn near a slick.
The relevancy to lightweight rotors or wheels is that it is an upgrade that is usable on a day to day basis, not something you pull out of the attic for track day.
Something like this for example: http://www.mickeythompsontires.com/street.php?item=SportsmanSR