There's a huge thread on this on TLW, but like a lot of figures on their own, they could say one thing that with further data or placed in a different context it could easily indicate something different.
That figure and other snippets I've read, for example referees being demoted to ref in divisions they haven't appeared in for a number of years, or not getting a Manc game for a long period of time after Taggart's complained publicly about them 'appear' to indicate there's 'something in it'.
However, you would need a whole lot more data to be sure there really is something underhand.
For example with Webb, what percentage of matches has he officiated in for all the other clubs? What is the percentage split for penalties given to other clubs, and in comparison with the number of times he's officiated over a club's matches. For example if he's only had 3 Arsenal games, and they were all against teams where they had much less possession than normal, and had very little possession in the opponents' defensive third of the pitch, and most of that was outside of the penalty area, and they had a weakened team in regards to players that would normally get in and around the penalty, then you would expect the percentage of penalties awarded by him to Arsenal to be very low, if any.
Likewise with a referee 'appearing to be 'demoted'. Was there a shortage of referees available in that league due to illness or work commitments? Did the fixture list fall in such a way that certain refs couldn't officiate certain games because they either have some declared interest in the club (ie support them) or they live too close to the ground to be awarded the game, and all those factors aligned in such a way that the division was short of referees and the said referee happened to be 'spare' because again there wasn't a PL game for him because of the same factors that created a shortage in the other division.
I've read all the articles mentioned both here and on the TLW thread and there does appear to be 'something' in it but without a whole host of other data around the examples and comparisons using the same data to look at other teams, it's hard to say definitively that there's indeed 'something going on'.
Take another example, Mark Halsey. How many times has he reffed a game where he's 'missed' or 'chosen not to give' a more obvious penalty and then given a 'soft one' to the opposition?
Or take a referee that sends off a player with a straight red for a 'dangerous' tackle. How many times has he done that, how many times has he awarded a yellow, or no card at all, and are the tackles of a similar nature consistently punished the same way or is he inconsistent in what punishment he dishes out? Also, what was his position relative to each tackle and is his positioning (good or bad) a factor in what punishment he dishes out or does he get his positioning consistently right or wrong and is there a pattern between position and punishment?
Most of us would say that the Mancs appear to get more soft penalties, fewer soft or 'nailed on' ones seem to be awarded against them, and especially at Old Trafford. They seem to get more favourable treatment all round off certain referees, their players seem to avoid punishment more often and Taggart seems to be able to say what he wants with less punishment handed out to him.
But how much notice do we take of other teams and their all round treatment and behaviour?