rentalcars.com UK covert rental conditions, Internet

I am an 80 year old Aussie and will be visiting USA in September 2013 to be with my daughter and my son-in-law who holds a USA driving licence. I booked a rental car in Australia from Dollar rentals Manhattan NYC, which is under  rentalcars.com umberella paying a $65.00 deposit. I then saw at the very bottom of the booking page view ts&tc conditions in tiny print. It was then I discovered that my son-in-law was not permitted to drive the car as he held only a USA divers licence. I then cancelled the booking as he was to be the primary driver which resulted in a cancellation fee of A$65.00

I explained my concern by email to rentalcars.com and their response was they could change the booking dates and that the car should have been booked in USA which of course it was. All terribly confusing and when further details were requested by me they bounced my emails Question why would my son-in-law not be permitted to drive the car and far more importantly why would such a condition be covertly hidden when it is vital to the booking prior to lodgement. This condition should be emphasised prior to booking completion rather than hidden for the unsuspecting, many of us , to miss.