Why does D rely on a GC?

[maik klein via Digitalmars-d]

First of all I don't want to insult anyone on language design, I 
just want to know the reason behind the "always on" GC.
I know that the GC as several advantages over reference counting, 
especially when it comes to immutable data structures.
What I don't (correct me if i am wrong) understand is why every 
heap allocation has to be garbage collected, like classes, 
dynamic arrays etc.
Does a GC still have advantages over heap allocations that do not 
need to be reference counted such as the unique_ptr in c++?
The dlang homepage stats:

Destructors are used to deallocate resources acquired by an 
object. For most classes, this resource is allocated memory. With 
garbage collection, most destructors then become empty and can be 
discarded entirely.

If I understand it correctly it means that D has a GC, so most 
classes don't need a destructor anymore because they don't need 
to do any cleanup. I am not totally convinced that this would be 
a good trade off in general. Maybe someone could shine some light 
on this statement?