Why Lawyer Billboard Advertisments are Deceptive

I know you have seen those billboard advertisements on 95 depicting an accident victim saying So and So Law Firm got me $600,000.00 There is no better explanation of why Billboard advertisements can be misleading than this SNL skit.
http://www.nbc.com/saturday-night-live/video/attorney-ad/3457927
Why are some cases worth more than others? Did the amount on the billboard actually go to the client or were there medical expenses, legal expenses, legal fees deducted? These questions cannot be verified just from the billboard alone.  Like the skit, you don’t know what attorney in the firm handled the case, did you get Brodrick or Ganz.