Phil, the councils deem alternate weekly schemes a success because it is the cheapest and quickest way to increase recycling rates.
They are aware that if they can weather the initial storm of protest, people will after a while stop complaining - not because they suddenly realise the schemes are wonderful but because they feel their concerns fall on deaf ears. This is the feedback I have had from all over the UK.
A good question to ask your council is "What percentage of contamination do you have in the recycling bins?" My Council has been honest enough to admit that figure lies between 10% and 14%. It is not always accidental and, in fact, at least two councils have had to abandon fortnightly collections because the rate of contamination with general waste is so high. I would not recommend this action as whole lorry loads of recyclable materials often have to be landfilled, but I do understand why people resort to doing so.