Why so few built-in range types?

One thing that bothered me while looking at the range types patch is
that it seemed you'd been mighty conservative about creating built-in
range types.  In particular, I don't understand why there's not a
standard float8range type; that seems like a pretty common case.
I'd have also expected to see a standard textrange type.  What was
the rationale for leaving these out?
        regards, tom lane