Arrests in Europe, of people believed to have ties to terrorist organizations, average a couple of dozen a week, with occasional peaks at upwards of 60 or so. Convictions average one or two a week. Many of those who are not convicted can be detained for long periods without charge due to surprisingly stiff national security regulations in many countries. All this is only occasionally reported in the media (whether "new' or "old"), and has very rarely elicited comment from official U.S. government spokesmen, except on those occasions when a suspected terrorist actually is released. Far more suspected terrorists are left stuck in the European legal system, which is still imprisonment, with, or without, a trial and conviction.
The Europeans aren't finding and locking up all these people as a favor to the United States. Many of these terrorism suspects are beyond suspicion, having been caught with plans, or a burning desire, for terrorist acts against European targets. While the European media likes to play the war on terror as an American cowboy fantasy, European police and intelligence agencies know better. They interrogate the suspects, and even if you don't speak Arabic, it is clear they are dealing with people who mean to harm non-Moslem Europeans. It's all kept pretty quiet, but not a secret. The politicians don't want to enrage the 20 million Moslems in their midst. But they do want to lock up the thousands who want to be Islamic terrorists.