Installing through steam with DVD

First of all, I haven't previously had any problems with Steam. I am not adding yet another "Steam is awful" thread.

However... I bought the game retail so I have the DVD. I know that if I install through Steam, I won't have to actually have the DVD in the drive to play the game - great. Why, though, does Steam insist on downloading the entire game for install when the disc is in the drive? Why not install the game from the disc and then just download the update? Unfortunately I have a usage limit on my broadband and can't afford a 2 gig download.

I have now got myself into a real mess because I associated the game key to my Steam account but tried bypassing the download and installing from the disc. Now Steam thinks the game has not been installed. Can anyone help?

BTTT

Any comments from SI or Sega?

Aside from anything else, it seems bizarre to put this extra strain on the Stream servers when the DVD is in the drive for install.

I uninstalled my disc install and gave in and downloaded the game through Steam - I can ill afford the penalty charges I will now have.

I'm unsure as to the reason for doing this, sorry - not technical enough!

It's strange because the way to install the game in your steam folder with a dvd is simple :

insert dvd, autorun or launch the install if you have autorun disabled, then in the install menu, you will have the choice to install in steam folder, steam will launch and install from the dvd, you only need to insert your activation key.

That's all, is it what you have done ?

You could have forced it to install from the DVD: https://support.steampowered.com/kb_article.php?ref=5357-FSQM-0382