Here's my understanding of the situation:
When Mr. Smith posts a video Youtube, John Doe isn't expected to be able to retain a copy on his hard drive. John is only able to watch it displayed on a public webpage until he leaves making it a transitory act of infringement, so it's argued that it's a public performance and not a distribution. Therefore he can only be held liable for damages, since public performances aren't listed amongst the criminal offenses. Additionally, only the rights holder has the standing to seek those damages since it's a civil dispute and the judge only has to consider what's likely.
Mr. Jones on the other hand who uploads the file to his website is giving the show away to people who can keep it to practically use it however they want which counts as distribution. If Mr. Jones distributes copyrighted materials in manners that coincide with Title 18, Part I, Chapter 113 Section 2319 and Title 17, Chapter 5, Section 506. (I'd give a hyperlink but I'm a new member and thus apparently incapable.)
When this happens Mr. Jones can be held liable not only for the civil damages Mr. Smith would be liable for but also for criminal distribution if proven guilty beyond a reasonable doubt. It also counts as a felonious crime, giving the government itself standing to pursue enforcement of the law if it so pleases.
If S. 978 becomes law Mr. Smith will be treated exactly like Mr. Jones because public distribution will be added to the list of criminal offenses.
I'm a bit worried as to how it might effect fair use claims on Youtube because in fair use is a bit nebulous and relies mostly on the court's opinion. Fair use typically exonerates copyright infringement claims, however if a predefined dollar value is set, then the court might not have as much wriggle room to make what it feels is a fair determination as par what qualifies especially where certain videos range into the millions of view marks.
I'm also concerned as to how the dollar value is defined: Youtube's advertising revenue? The cost of a license to stream? Retail value of the work multiplied by the number of views? It isn't clearly stated so it might just be whichever's highest, which may in turn have a chilling effect on 'viral' video sensations.
There's also some concern about whether simply linking videos counts as a 'public performance' in addition to uploading them, since the term isn't precisely defined. Granted it's unlikely that you'll link a single video enough times within six months' time to trigger criminal liability but it's not wholly impossible. Using an iTunes music video value of approximately $2 a pop as a basis, you'd have to 'rickrolling' people somewhere between approximately 500-1250 times would just about do it.
(Okay that's a bad example as it might 'already' be covered by S. 2319A which covers the performance of music and music videos specifically and doesn't even state a specific dollar value. However it's still the best practical I can come up with under the circumstances.)
Does that help?