tuple(...).each error; why does foreach work and std.algorithms.each doesn't ?

[wjoe]

Consider a function to format the parameters of a function call:

pure nothrow string fmtArgs(ARGS...)(ARGS args)
{
    string result;

    // 1)
    foreach(a; args) {
       result ~= a.to!string;
    }

    // 2)
    args.each!(a => result ~= a.to!string);

    return result;
}

In my mind, if something works with foreach, it should also work 
with std.algorithm.each.
However if I try something like 2) the compiler complains with 
error: cannot deduce function from argument types !()(uint, 
int)...

Technically I'd like to transform args into a range/array of 
strings but I'm not smart enough to understand the error messages 
these functions in std.algorithms produce.

How is 1) different from 2) ?