There is more information to search for, this is why there are more results. Google searches and shows every site for all 3 words (most relevent), then 2 combinations(not as relevent) then 1 on each to show ALLLL possible results for the query (usually hardly any relevence).
This explains why there are more results for the 'Bluray dvd burner' than 'bluray burner'.
It give no guidance that 'Bluray dvd burner' is BETTER...
BUT... if you put ""s around them, this gives an indication as to which is better.
"Bluray dvd burner" is not as good as "Bluray Burner" because "Bluray burner" shows more results than "Bluray dvd burner" when they are encased in ""s