IE 8 Browser Question

Okay i seem to be confuse here with ie8, I'm running windows 7 ultimate and it comes with
and ie8 comes with it what i dont understand is that some sites that i go to detect my browser
as ie7.. I then went to this site:
Peacekeeper - The Browser Benchmark to do a check and it said ie7

now heres a screen shot of it.. Okay i then went to microsoft:
Install Internet Explorer 8
and it said ie8 cannot be installed on this platform

can anyone explain what the problem is here.. serial was remove for a reason

After turning compatibility mode off from all sites and setting it back to standard
settings i end up getting this result:

User agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1;
Trident/4.0; SLCC2; .NET CLR 2.0.50727; Media Center PC 6.0;
.NET4.0C; Tablet PC 2.0)

So i guess its not wise to have compatibility mode on all web sites then?

many thanks for your help on this. reputation tap for you