Well, I am. Warwick, Durham and Bristol are all great unis, but they don't quite compare to many of the US' top schools. Not yet. Maybe they would be in the long run. I know that Warwick is a very progressive institution and it's getting better and better every year. But right now, it's not yet in the league of UCLAs or UMichs or CMUs. Maybe in time it will be. But right now, not yet.
UCL has a slightly better global appeal than have Warwick, Durham and Bristol. I believe it should have been ranked above the 3 in the international arena.
Manchester is another UK uni that should have ranked very well in international league tables due to its strong research output and great postgrad programs.
The thing is, UK unis are viewed differently outside of the UK. For example, Warwick and UCL are neck-and-neck in the UK. However, on international level, UCL is viewed ahead of Warwick.