COD Modern Warfare 2 downloading after disc install

[Stapler42]

I just bought COD MW2 from the steam store today. It wanted to download 11.3 GB to install (the whole game I'm guessing), but I had a disc copy from when my older brother bought it close to when it came out. I installed from the disc because my internet connection will take like a whole day to download it. It says it is installing 11003 MB from the disc, it finishes and I go to play it but it still wants to download the 11.3GB. I deleted local content and reinstalled but it happened again, I deleted everything in steam except the .exe and steamapps. Installed and steam still wants to download it. It's not downloading to a different call of duty folder, I checked.

Any help would be greatly appreciated as I do not want to have to download 11.3GB.
And it is actually downloading it's not just like verifying or something.

Thanks.

[Balot]

My guess is that it's downloading the version including all the patches that came out over the years.