Apply and Plus have different precedences:
In[1]:= Precedence[Apply]
Out[1]= 620.
In[2]:= Precedence[Plus]
Out[2]= 310.
The higher the precedence, the tighter it will bind a function/argument pair. This matters only when using infix notation. Bracketing overrides the precedence pairings.
Prefix notation is not affected by precedences, since the syntax itself decides order of evaluation:
Apply[Times, Plus[a, b, c]]
Postfix notation also generally works Ok:
a + b + c // Times @@ # &
