About the car analogy: You can modify your car in any way you like. There is no law against modifying your car. However, depending on the modifications, you may no longer drive it on public roads. The legislator determines in which case you may or may not use public roads after modifying your car.
In the case of PS3 however, Sony, not the legislative body is trying to to tell you what you can and can't do with your hardware, in the privacy of your own home. Notice the difference? Sony is not the legislator, and it is not up to Sony to determine what you can do with stuff you own, in your own home. What they can do is bar you from using their online service PSN, which they own, with a modified PS3. And despite of what they'd like to make you believe, this really is the limit of their power over what you can and can't do.
EDIT: typo
"Well certainly with the Xbox 360, we had some challenges at the launch. Once we identified that we took control of it. We wanted to do it right by our customers. Our customers are very important to us." -Larry "Major Nelson" Hryb (10/2013). Note: RRoD was fixed with the Jasper-revision 3 years after the launch of 360
"People don't pay attention to a lot of the details."-Yusuf Mehdi explaining why Xbone DRM scheme would succeed
"Fortunately we have a product for people who aren't able to get some form of connectivity; it's called Xbox 360,”-Don Mattrick
"The region locking of the 3DS wasn't done for profits on games"-MDMAlliance
