Do the rules as written make Assault weapons and Pistols useless?
The Most Important Rule

Basic Rules, Page 6 Sidebar, Summarized:


  When you aren't sure of what's supposed to happen, talk with your opponent and apply the most sensible resolution that you can agree on.  If you can't agree, roll-off, and apply the victor's resolution.


The fact that this is labeled "The Most Important" implies that this trumps any other rule.  Additionally, it relies on sense, rather than interpretation.  It would not make sense for the rules to include exceptions which do not apply, regardless of how you interpret the "hard" restrictions on Advancing.  

As is true in almost any game, general rules are to apply until an exception says otherwise.  WH40k's version of this rule is "Do what makes sense", and an exception to the rules will only ever make sense if the exception can be applied.

Since the rules under Pistol and Assault weapons state they're an exception, those exceptions must apply, since it makes more sense to obey these exceptions than it is to accept they were arbitrarily added to the Basic Rules for no reason.