Hi Nikola,
In the AdWords user interface, the check boxes next to the items under Devices can be confusing because you can't remove them. I'll look into asking the engineers to fix that to make it less confusing for the next person.
At the campaign level, the only device you can exclude is
Mobile Devices. You can't remove or exclude any of the other platforms. In the API, you set the
bidModifier on the
CampaignCriterion Platform 30001 to 0.0. When you go to the AdWords user interface, you'll see that the
Bid Adjustment is now
-100%. To include
Mobile Devices again, you would set the
bidModifier to -1.0. Since that's not always easy to remember, we've included it in our documentation
here.

I hope that clears things up for you.
Regards,
Nadine, AdWords API Team