Well I'm English and my teeth are fairly crooked, but that's just me.
I had LOADS of dental work as a child and teenager, which pretty much saved me from having an actual deformity of the mouth, more or less - so I'm lucky in one way, but even all that work wasn't able to save me from having crooked teeth.
I can only say that they are a lot better than they would have been without the work. Basically my top jaw was too narrow for my teeth, and it had to be artificially widened, and then some work on straightening my teeth - but over the years some of them have 'settled' back a little.
Also my teeth are quite yellow, but that's not due to lack of brushing - I try and keep good dental hygiene, always brushing at least twice a day and for a good long time, so I reckon that's just the natural colour of my teeth. (Maybe I drink too much coffee and tea!) I'd like to get them whitened one day, but there are so much more important things to spend my money on in the meantime!
(And I don't want to go for one of those dodgy bleaching treatments from some unregulated place.)
My teeth are also pretty weak... I think they are just 'not great' hereditarily/genetically and I just had bad luck...