As HHTel has stated, no laws have changed. It has always been compulsory to wear helmets, both the driver and the passenger. Things are changing but not very quickly.
When I first moved to Hua-Hin, very few people wore helmets, whereas nowadays most people actually do, at least in the center of town.
From what I've seen, the MIB never crack down on passengers riding not wearing helmets, and they don't tend to give a damn how many people you have on the bike.
With a saleng (fitted side hack), the driver must still wear a helmet. Not sure about passengers, but again, I've never seen the police fine because passengers aren't wearing helmets. A short while ago, they required all saleng owners to get a document from the police stations confirming whether their vehicles were for business or private use only. This too was never enforced. I have been through countless police stops since, where loads of motorcyclists were being fined for no helmets and etc, and I've never been stopped yet. Most times, I just get a smile and a salute.
I know many people will disagree with me, but as I've said before, the fact that Thailand has such a "live and let live" attitude, is one of the biggest reasons I'm still here. We also need to remember that most of the MIB are no different from your average Thai, and their mothers and fathers are probably also driving around with salengs and etc.
I think Roel hit the nail on the head when he said people complain when laws aren't enforced, and then they complain when laws are enforced. I wonder how many of us will want to stay here if Thailand becomes just like the UK, USA, or etc?
I guess I just find it hard to believe that 99% of the Farang who live here, moved here thinking that Thailand would be like their home countries within a year or two.
We all knew about helmet laws, and that most don't abide by those laws: we all knew about corrupt officials; we all knew about soi dogs, and yet a few years down the line, people start complaining.
Welcome to Thailand, and let's hope it never changes, at least not while I'm still alive.