Basically, dulia is veneration, and hyperdulia is ‘super-veneration’. The Church considers the special nature of the Virgin - most blessed amongst women, mother of the Lord, and so on, makes her a worthy receipient of this, and seeks to reflect the heavenly court where Mary is Queen of Heaven alongside her Son, who is King ( for more on this see Solomon & Bethsheba, and the wedding feast of Cana).
However, Mary does not receive latria, the term used to express the adoration due to God alone.