I have a question about the classics version of games, (with the silver background and the box art reduced), do they include additional content like DLC or they are just the same game again?

Just wondering because I found dead space classics version for 15 pounds and the regular one for 13.

Thank you.

Nope, it just means they're a well receive/reviewed game. Sometimes you get GoTY classics and they do include DLC, but unless it says stuff like 'GoTY' 'Ultimate edition' 'Special edition' (etc.) on the box art it won't add anything extra.