not quite getting it

This might be a strange thing to get peeved about, but it never fails to rile me...when people adhere to a strict set of religious doctrine, but don't quite follow it properly.
I realise that sounds odd, given that I would rather there were no religions since the belief in a divine creator who sits on a cloud watching and judging our every action is really rather stupid, but I get really wound up with the in-your-face religious types who fail to follow the rules which they claim they must live by. I mean surely, if the bible/koran/torah/whatever is the "word of god" then you can't just pick and choose the bits you like. But then despite the bible proclaiming that god does not like his flock to wear clothes made of mixed fibres a great deal of people calling themselves christian will wear a poly-cotton mix. Similarly I know many christians who do not fast for lent, who will eat meat on a Friday and so on. Obviously there are many more examples, but you get the gist of what I mean.
I am finding though that I am becoming increasingly annoyed at the muslim population who seem to want special or preferential treatment but fail to actually follow their own "god given" rules. A good (or bad) example is a former friend who converted to islam but had never once prayed or attended the mosque because it was "dull". She did however don a hijab and veil whenever she went out, and subjected her baby son to circumcision, despite eating sausage rolls and drinking alcopops in the privacy of her own home.
In the koran, the passage that has been interpreted as telling women to veil does not actually tell women to veil. It says they should dress modestly, not show off their "ornaments" and not strike their feet when they walk. If women do veil they are only supposed to do so after puberty (although some interpret this as after the age of 9, the age of Mohammed's child bride when he consummated their relationship for the first time. Interpret that as you will its all there if you wish to go and read it). So what I don't understand is these women who claim to be so devout, and to follow the religion so strictly who actually flout the rules laid out within the koran. I have lost track of the amount of times I have seen women wearing a full burka outfit, clip-clopping down the street with the unmistakable sound of a woman in high heels. I have seen girls still in pushchairs who are wearing a hijab. I have seen muslim (and jewish) men and women give their children jelly sweets that contain pork gelatin. I saw an elderly muslim man sitting on a bus eating a packet of frazzles bacon crisps.
I just don't understand which parts of the religions tell people to pick and choose which rules they follow. Surely it is an all or nothing thing? And if you are going to pick out only certain rules to follow, then why pick the ones that harm others, like circumcision, or veiling young girls?
I guess this rant was triggered by the woman I saw earlier wearing a leopard print burka. Go figure.