Alias parameters for templates does not accept built-in types

[Deokjae Lee]

import std.stdio;

template T(alias X) {
}

void main() {
    writeln(typeid(typeof(T!int)));
}

dmd 2.048 on linux produces an error for the above code.

Error: template instance T!(int) does not match template declaration T
(alias X)

Built-in primitive types cannot be used as template alias parameters. 
User-defined types like structs or classes work well. I think this is a 
bug and reported it.

http://d.puremagic.com/issues/show_bug.cgi?id=4639

However, I got a reply that the behaviour is intended.
I think the limitation that the built-in types are not accepted as alias 
parameters for templates is not beautiful :(
That's a kind of lack of symmetry and practice :)
I'd like to know the reason of such a limitation.