It all actually due to price increases, whether its shortages or not or government intervention to reduce obesity, if the price of the ingrediants goes up the cost of manufacturing them goes up as well with gas and elecy costs so the to keep them the same price or as they see it affordable, they reduce the size to compensate, then they put the price up to cover profit.
I remember a mars being 68g, now they are 33.8g (if the 10 pack is the standard size bars at £2.00) - so I buy asda's 6 pack at 38g each bar at £0.85p, taste the same, get more per bar and pay less, 12 for 30p less for 10, you do the maths