To expand upon Kai-V's excellent response, the reason there are slight differences in weight is due to the fact that these ARE only toys, and therefore the quality control is only to keep the weight within certain parameters.
For what it's worth, there may be a slight difference between different wheel numbers as demonstrated in Kai-V's last link, but it's rather miniscule. My A2 Basalt is apparently heavier than my A4 according to my kitchen scales, but again, it's not a huge difference (1g, with a +/- 1g accuracy, it could be nothing ). It's again worth noting that that's not the Lot number isn't the factor, but the number on the wheel. While certain numbered wheels may be more common in certain lots, but even then, it's not guaranteed, and I wouldn't pay that much extra anyway.
I wouldn't pay that much extra, but some people would. That may be the price difference.
For what it's worth, there may be a slight difference between different wheel numbers as demonstrated in Kai-V's last link, but it's rather miniscule. My A2 Basalt is apparently heavier than my A4 according to my kitchen scales, but again, it's not a huge difference (1g, with a +/- 1g accuracy, it could be nothing ). It's again worth noting that that's not the Lot number isn't the factor, but the number on the wheel. While certain numbered wheels may be more common in certain lots, but even then, it's not guaranteed, and I wouldn't pay that much extra anyway.
I wouldn't pay that much extra, but some people would. That may be the price difference.