Some characters are small enough to duck under his high projectile.  Basically, it works as a handicap since the high projectile won't hit low fireballs (like Rugal's or Iori's).  Also some characters have slides/other moves that won't slide under the low fireball.  For example, Vanessa's special dash goes through most projectiles except low ones including Roberts.  It's a different play style that makes Robert a little different than your average Takuma.

Lariat Drop is unblockable.  The AI is able to block it because the AI is broken.  It can block even when you aren't attacking (which is impossible for a human).  As a human player, you won't be given the option to block.  I'm hoping the AI fix will resolve some AI issues.  Never take AI actions at face value when testing.