numeric type conversions

Hi,

I should cast field of 'text' type to the 'numeric' type,
but PG output error message: "ERROR:  Cannot cast type 'text' to
'numeric'".
I had tried to use conversion to type 'float' and all works good,
and now I must write quaries like next one:
    SELECT price::float::numeric .... FROM priceValues WHERE ...

Why confusion situation between types numeric, float and text ?
There are any reasons to not to write default type conversion
from 'text' to 'numeric' in the PostgreSQL 7.3?

Imho, almost all types should have default convertors from and to
the 'text' (varchar etc) type..

Thanks,
Ruslan A Dautkhanov