The question of legality related solely to its use within London. There has never been an issue outside of London and I imagine that before Uber other taxi firms used apps, it was just the threat to black cabs that brought this action.
I find it ridiculous reading about all the issues Uber have had in London and the black cab drivers pushing back so hard.
[1] http://www.manchester.gov.uk/directory_record/72535/new_hack...
As richthegeek said, all the private hire taxis here have a yellow rectangular sticker with the company name on it. There's strict limits set by the council for branding, car colour, car age, etc.
I'm surprised there wasn't any more pushback from the entrenched firms here, as they've spent the last 10 years treating both the customers and drivers like absolute dirt.