call me cynical - but I suspect the list was made up by some dillitante during the Victorian era;

silver, gold and diamond for 25, 50 and 75 for the 25 year marks seems to have been around a bit longer. I suspect the others were just filled in in increasing order of $$ value. "Crystal" in the anniversary list refers to glassware/tableware rather then rock crystals.

The lists I've found don't seem to be all that standardized anyway - aside from Paper as 1st (and many people feel that should be "folding paper - ie money) silver, gold and diamond.