black cabs are licensed, regulated and they can offer a "hail and ride" service
the drivers have also spent time and effort as well as a considerable amount of money doing "the knowledge" for at least 3 years as well as having to pay through the nose for their black cab, which is why their prices are so high (although they claim that the prices are set by the london carriage office)
everyone else is just a man and a car and you have to prebook
uber have got around this by their clever little app and that is why the black cab drivers are pissed off
but the last time i use a black cab he not only took the long way around, it cost me £19 when the same journey by bus would have been 80p (and it would have taken about 15 minutes longer) so i'll not use one again
the last time i used a minicab i had to wait 35 minutes for him to turn up and then he was driving like a twat, so i'll only use them again if i'm seriously desperate
that said, i used to be a minicab driver way way back in the day, but only because it was cheaper to insure my cossie as a cab and pay monthly (£60) as opposed to paying £1200 for it fully comp for a year