Firstly most babies do have stores of vitamin D for the first few months; the big exception to this would be if the mother herself is extremely deficient during pregnancy, and perhaps in cases of prematurity. Also rickets starts off only in older toddlers/children and is due to various lifestyle factors, it doesn't affect young babies, I was reading a paper by UK government scientists online the other day and it said most of the new cases of rickets were due to certain lifestyle factors as opposed to the strength of sunlight in the UK-the majority of cases of rickets occur in those of Asian or African background, where neither mum nor baby/child ever go outside and the family have a strict vegetarian or vegan diet-including mum never taking supplements either.
Other factors in the cases of rickets were EBF babies of already deficient mothers being weaned onto solids late and onto an extremely restricted diet. Another reason why rickets is common in some Asian communities is to do with the daily consumption of unleavened bread; there is something in unleavened wheat that binds to calcium and vitamin D, preventing them being absorbed properly. This is one reason why rickets is still very common in some areas of the Indian subcontinent despite there being no lack of strong sunlight in most places. I used to work with an elderly Indian lady (hindu from gujarat) who had severe rickets as a child, and gujaratis do tend to eat chapatis as opposed to rice with meals. I do know of a child who had rickets and this was because the mum never went out with the baby; she was suffering from severe PND and lived in a dodgy high rise-he had to have high level supplements for a while but all her other kids are regularly tested because there is some indication that some people are genetically more prone to vitamin D deficiency, all of them have the same diet and have never been given drops, yet they are all fine. The main factor in that is my friend moved to somewhere where it was easier to get out and about and made sure to get out at least three times a week with the children.
I was reading as well that some of the studies that the US and Canadian government use to recommend supplementing babies with vit D are based on the fact that in very extreme cases; small babies can suffer seizures due to having no vitamin D stores and not receiving any vitamin D through mums milk either, from what I was reading though some of these were based on African American, formula fed babies in detroit some years ago when the requirements to add vitamins to formula were not as they were now so the formulas either had no added vitamin D or not enough; and they were not based on BF babies at all. As far as I know the most up to date advice in the UK is for mum to take a 10mcg supplement of vitamin D throughout BF, and that certain babies may need supplementation after 6 months; but not before xx
LO has never had the drops and I rarely take the tablet. We don't drive, so we're always outside, and I'm not convinced of the value of supplements. I do take them if I remember though, as they're not going to cause any harm. Very much your decision 
