I believe that there are two different pools of stats that can be added, and I believe the dividing line is similar to prefixes/affixes in D2; this item has 1 prefix (Crit damage), and 3 affixes. Legendary items are rolled the same way, except their affix pool contains legendary powers, natch. Amulets and Rings seem to have 4-6 in total, but its usually 2 different types of resistance and then some tertiary stats.