The special vehicles thing is very rare. London is the only place I have ever seen it (though admittedly I have yet not been everywhere). Everywhere else, taxis are just regular cars with a meter and a taxi sticker on them.
They've adjusted but limo companies also used to gravitate towards the various body of frame models including other variants on the Crown Victoria. Apparently they were very attractive for high-mileage uses because of maintenance/rebuilds.