I'm sorry but one hour from NE Birmingham to Central London? Either you go by helicopter or you need to be caught by the police... It's about 130 miles! It takes about 2 hours, or 90 minutes by train from central Birmingham.
As for how difficult it is to get to Wembley, I work in central London and commute past it daily, I know exactly how "difficult" it is to get to... I'd agree that some parts of London are not well serviced by public transport and it takes longer than it should to get from A-B, it's one of the reasons I loath going anywhere SW... Wembley isn't one of them though,it has two major tube lines going past it, which service plenty of major train stations (kings cross, Waterloo and Euston from memory, most arrivals into London won't even need to change tubes).
You're also forgetting that over half the population within an hour of Wembley are not in London, they are in the commuter towns around it, with easy, fast access to London, but journeys of 2-4 hours to get to Birmingham. As an example it takes 2 hours by car to get from North Herts to Birmingham, but 20 minutes to Central London. For those living in Kent, Surrey and Middlesex it's the same or more, yet again much less to get into London.