"I was just wondering why the level restriction was even mentioned as the restriction is on the charts?"
I know you asked HD the question, but I thought I'd offer my opinion.
As far as I'm aware the charts (AIP) only show the profile of the stepped climb i.e. climb to 3000', level off for a bit, then further up to 4000' once round the corner. These charts do not hilight the fact that the climb should be STOPPED at 3000'. Therefore the level restriction "mentioned" by the tower controller is an instruction overiding the SIDs' climb profile i.e. climb to 3000' and only subsequently higher once cleared by ATC.