If you login with a Windows Live account that is populated with that info it will populate all devices logged in to that account. My two desktops, RT and Windows phone share the same account. Make an edit on one and it goes to the others.
Can you clarify please if you are talking about the 2 different contact applications native to each platform synching or if you are talking about a desktop synching with the tablet?
My desktop and surface tablet sync contacts just fine. I have no issues within that. However the 2 applications running on windows 8 regardless if they are on Surface RT or my desktop do not talk with each other.
I could not get “windows contacts” (an app that exists in Windows 8, 7, etc) to sync with “People” (an app that exists in Windows 8, windows live, outlook.com). The data would not sync. I needed to export the CSV file and re-imported it as defined above.
I’ll test this some more tonight by generating some fake contacts on my iPhone and trying to force comms.