They are making polite conversation or can't think of anything else to say. If someone's had a really obvious haircut, however, it can be rude not to mention it.
This reminds of when my dad told his friend he couldn't go to a football match because he had to go to his grannys funeral.His mate said "Why? Has she died?"
mybe they're related to my wife, 'are you ****** again?' 'are you going down the pub again?' and various question allong that line. if mastermind did questions on "the bleedin' obvious" 'er indoors would win. yeh, i know i'm a sexist pig but i do bring a packet of pork scratchings home for her so i'm not all that bad!
these are leading questions which if answered reassure the speaker that conversation is ok.
in regards to comments about the weather, it is so ingrained into most English people to talk about the weather that this sort of question/statement can be viewed as just another way of saying hello
It's called small talk. Folks feeling the need for conversation use these (hopefully) benign subjects to get a conversation going. And most folks (especially women) are waiting for you to notice their new haircut, clothes, weight loss, etc. It's only polite to comment on it.
Surely it would be more ignorant not to speak to someone and ignore them than starting a little small talk. Its often commented on how people do not talk to each other at bus stops etc anymore. No wonder when they get called thick and ignorant!!!!
The answer is far more clever or sinster. Asking about the weather is smalltalk but once you start talking you reveal lots of other things for instance - your accent.
So infact you're politely finding out about someone without being too blunt. This is a hangover from our past of course but can still reveal if someone is 'one of us' and it works for everyone of all backgrounds.