An interesting sub-genre that is generally full of controversy, but a very valid sub-genre. Often "genuine" news photography would drift into areas of pap work e.g. being able to zoom in on private papers being carried to cabinet meetings or press conferences for instance, or "door stepping trials and enquiries for mug shots of accused/witnesses etc through to shots into moving prison vans or cars. Small step from those skills to papping a celeb in a merc or stepping out of a restaurant, and often easier - the vast majority of celeb pics are co-ordinated by P.R. companies or representatives of the celebs themselves. There are plenty of A-list celebs who live a life outside of the incessant media bubble and one doesn't get to see what dress they are wearing today - mostly, there is a reason for that. It is a game where both sides know the rules but sometimes forget them and will get more prevalent with the on-line content to fill.
The high-end stuff will generally be as a result of a tip-off from a well cultivated source, often that will have involved some degree of investment along the way, mostly do not result in anything but occasionally gold will be struck with a genuine exclusive.
It can be incredibly boring and tedious with small frenetic bursts of action but the camaraderie of the regular photogs used to be something to experience - right down to sharing negs if someone missed the shot! Not for everybody and like most jobs, it has its grey areas but if there was no market for the images...