I mean horses winners of group 1 races, too!
I definitely think that a winner of the Grand Steeple-Chase de Paris, or of the Cheltenham Gold Cup, of the Aintree Grand National Steeple-Chase, and so on, has all rights to be included in this database

Let's look at an exemple.
PINEAU DE RE won the Grand National Steeplechase of Aintree in 2014.
He wasn't a pure thoroughbred. His sire MARESCA SORRENTO was a thoroughbred, but his dam ELFE DU PERCHE wasn't.
Her seventh dam ENGLANTINE, born in 1904, was registered in the Selle Francais stud-book.
Ok: let's avoid to include "impure" horses in this database, let's put him in the brother site "All Breed Horse p.d.".
But if anyone has the insane curiosity to know the parents of the winner of the Grand National Steeplechase of Aintree in 2014,
at least you ought to redirect him to the brother site.
Of course this solution implies that the brother site "All Breed" includes all the thoroughbred horses having one non-tb descendant who won a group race.
Don't you think that to admit some "impure" subjets in the pedigreequery.com db is definitely easier?