Cartier and charging for grocery stop

[skiwee1]

I booked Cartier for our October trip as they has a good special. It only cost $45 extra to get a limo one way and a towncar on the return trip. After booking online they called me and told me that it would be an extra $15 for the grocery stop since I'm using the limo on that leg of the trip. Do all companies charge extra for stopping in a limo? I know the stops are free usually if in a towncar but I have never heard about it being extra for the limo to stop. What would be the reasoning behind this anyway? I just may be looking at another company if this is the only one that does this. We have only used Tiffany in the past and never a limo. Thanks for any info!