Joy of Radio Control

I bought two little Radio control Cars for Christmas with the hope of a race or two.
but when I opened them and got them set up?
Oh joy they are on the same frequency 27.145Mhz why?
There are 6 different Channel I think but some say 30?
http://www.storacingproducts.com/support/radio_frequencies.pdf
So why all on same frequency.