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Oliver,
You are sounding off on a subject you have little knowledge of when it comes to cobbles, Bonds is a concept from Bricklaying and as you know (because we were both at the same lecture by Carlton Reid) the majority of London roads were paved with wood up to the Second World War. Cement and fly ash alone would make poor cobblestones, fly ash is generally added to concrete as a cement substitute and as a way to slow the speed of set and heat generated. There is a good website on how paving is laid here
Zebra_Cyclist
It's not only a matter of the bonds (many old cobbles are not bonded, just laid very precisely), but also of materials. Granite is far too hard-wearing and will still stand proud when all the bonding has already been washed/scraped out. Older cobbles were made from a mixture of cement and fly ash (a waste product of the coal power industry). They generally wear smooth and are much better to ride bikes over. That material was also cheaper than granite, meaning much larger, less easily shifted setts. You can always see in streets where these still exist how we've lost the art--you only have to look at repairs, which are generally much lower quality/with granite/hard to ride.