The Hometown Umpiring Advantage - Why?

OK, a quick question; why do home teams get such an advantage in 50/50 calls from the umpires?

If we look back over recent series, almost every time the home team has got the rub of the green in the dubious (and sometimes not even vaguely dubious decisions). Australia certainly cannot complain, as we benefit from this in home tests, but likewise, India and England have had similar 'luck' when playing at home. It has always been accepted that this happens, however, I wonder why this is.

What is the reason for home teams getting the home-town decisions? What impacts upon the umpires to have this happen? If we assume (and please do) that the umpires are not intentionally biased towards any team, and make the decisions purely based upon what is in front of them, why do they make errors that consistently seem to favour the home side? Even if you accept that that some umpires are incompetent, in theory they should make an equal number of errors and neither team should benefit.

Is it due to the crowd's influence? Is it due to home teams putting subtle (and not so subtle) pressure onto the umpires? Is the conditions that allow home players to perform in such a way as to minimise the appearance of their guilt (i.e. in Australia and on bouncy pitches, Ponting's front foot lunge appears to get him outside the line of off-stump and umpires tend not to give him lbw). Is it a statistical illusion, based upon the fact that the home team is generally more likely to generate more close appeals and therefore get more decisions in their favour?

Perhaps we also need to include a point about our own biases in terms of interpreting umpiring errors as well. I reckon Australia has been clearly worse off in terms of decisions in the current Ashes series (not that this has had an impact upon the results - Australia has played like shit and doesn't deserve to win). However, I am naturally biased towards interpretating 50/50 decisions in a certain direction, and to therefore see things in a different light to what an English supporter would do. I can remember Nasser Hussain (for example) praising the umpires in a previous test for giving an LBW against Australia that Hawkeye showed to be clipping the top of leg stump. And only a day or so later, Nasser Hussain again praised the umpire's decision in not giving an English batsman out to a ball Hawkeye showed hitting almost the exact same spot. His interpretation of an almost identical incident was influenced by his own bias. Perhaps we are all just similarly guilty.

Of course, the home town advantage is not limited to specific sports or countries. It occurs in soccer, league or whatever sport you care to mention. However, I can see why the home town advantage plays more of an influence in certain games such as league or soccer, where the home town fans can respond instantly to off-sides, forward passes etc, and the umpire/ref must be affected (to some extent) by that pressure. But in cricket, most of the spectators are not in a position to place instant pressure onto an umpire, and the decisions occur after consideration (and not during the flow of a game such as soccer, AFL etc).

I would be interested to see what the ICC Umpiring Panel thinks about this one, however, they would undoubtedly tell me how how high the standard of international umpiring is, and how they get 95% of all decisions correct. Yeah right - they must go to the same school of media relations as Andrew Hilditch.