yes well i also do not smoke however high blood pressure is also a common factor, no offense but excessive consumption does not typical cause anything such as calcium spurs or deposits in general.
I am not sure they know for certain but any medical conditions can also add to this, bottom line is calcium on the placenta signifies that the placenta is ageing and becoming near term. and this is common when you are 37 weeks + but obviously at 28 weeks there is obviously something that needs monitoring.
It doesnt mean in subsequent pregnancies you will get it, nor does it follow the scientific pattern of what supposedly causes it (but honestly in pregnancy what actually does?)
I had pre eclampsia with my first baby and never had any other problems, i smoked before and gave up when i found i was pregnant and my placenta was fine.
This time round I gave up smoking christmas 2009 and fell pregnant fed/march time so good few months after and in fact i had scans at 7/12/20/23 weeks and everything wsa fine, then 28weeks high bloody pressure and this calcium deposits.
Bottom line is if they think its serious enough they will do something about it but apparently the main concern is the babies growth as the placenta ageing means that babies growth can taper off. The sonographer/MW or a consultant would recommend re scans where any doubts may lie.
I certainly would not consider against another pregnancy just because of complications first time round as all pregnancies are different.
Anyway rambled a bit there, I will keep a post going if i find out any further information.