Ian I wasn't saying that it all revolves around industry hence why I cited the London example. i.e a Financial Centre. You mention Manchester's financial sector which is growing but still lacks behind Leeds at the moment. Even so, Leeds isn't a powerhouse either.
Again, with regards to the University district I am well aware of the fact that Manchester has the biggest student population in Europe but does that necassarilly make the City a powerhouse? I don't think it does.
The BBC may lead to something big but MediaCity is still very much in it's infancy and Manchester United, whilst a powerhouse in it's own right in sporting terms, comparatively speaking it does not create a huge amount of money for Greater Manchester. In fact you can argue that much of Man Utd's money doesn't touch Greater Manchester in any way, shape or form.
Like I said though, when I think powerhouse I think London, Dubai, New York etc. I would regard relatively few Cities as such.