California - 55mph towing a vehicle?

I am making my first trip down to Palm Springs from Vancouver Canada and have been very comfortably travelling 65 to 70 mph through Washington and Oregon with my 2011 Yukon GMC and my 2007 and 2720SL and I just came through the California border today to Redding California and there are signs on the highway that say- Any vehicles in tow - max 55 mph, which I assume means trailers. Likewise I have kind of cut my speed down from 65 - 70 to about 60 mph with my relatively new 15 inch marathons at 60psi with no problems. I notice in Oregon and even California the semi-trucks travel about 10 mph over the posted speed limit. I agree that 65 mph is a good safe speed for a trailer, but it seems odd that you can go 70 mph in Oregon and only 55 mph in California. Has anyone every got a ticket going 65 mph in California? or do I need to keep to the the 60 mph?