It's not really a trick...
It's just the way the courts work. It's the same reason why OJ is free...
Beyond 'all reasonable doubt' is needed.
As refusing to do something and it being declared as an automatic admission of guilt... that conflicts with your rights as a citizen and the law of innocent until proven guilty. Maybe the UK is different, but freedom is a big deal in the US. For better or worse.
They'll take away your driver license (until it's settled) if you refuse, and take you to jail (again until it's settled, or bail.) But, they are going to do that anyway, if you fail the breath test. Anyway, the only people that truely slip through are those that can still carry themselves well. You still have to pass their other tests with big brother watching, all the while.
And here is something else... even if they are convicted and have their licence suspended... they can still apply for a (I don't remember what it's called) something license that allows them to go directly to and from work. Then if they are caught, it gets serious. How serious, I don't know. Don't know anyone that went that far.