Google could make themselves number 1 but they hate doing anything by hand in the SERPs, they want there Algo to detect and rank/ban stuff and they can sit back and enjoy life lol
If you were already on Google they couldn't really advertise Google.co.uk (or .com) to you as you were already on the site
Well first you clicked the top one so it could be just your preferences But secondly google ranks on votes and relevance and if google thinks another sites should be over them then they are. Another reason google isn't so bad