Samsung is, for the moment ay least, a multi-billion dollar company with huge pockets. Win or lose the cost of this type of court case is a blip in their budget. However for the defendant the financial risk is huge: he could lose his life savings on a case like this.
Isn't Youtube the defendant here? Google could step in here.
Nope, as long as YouTube abides by the terms of the DMCA, they are shielded from liability. This means they must take down the video when they receive a copyright claim, but must reinstate the video if the author files a counter claim. At that point, Samsung's recourse would be to sue the author.