I think I might have intended to post my earlier comment in the other thread running at the moment with similar content - mods, would it be appropriate to merge these?
In Europe, if a controller says "radar contact" then the implication is that you are positively controlled.
My bold highlights the exact issue I have with this system. Nothing should be left to implication or assumption. Terms of service should be stated clearly and acknowledged - it is important to note that this may not be that which was requested.
On top of the issue that
Glamdring raises, is the fact that radar coverage is not absolute. There are areas that I work traffic in where I have good SSR cover but no PSR cover - I cannot therefore guarantee that I can see all traffic as it may not be transponding. Further, there is no need for this traffic to call me (indeed, no need to be RTF equipped) as it is in class G airspace. Also, a lot of pilots (including those of some airlines on revenue flights, I might add) prefer the autonomy offered by a traffic service over a deconfliction service.