mlvl is the notation for monster level. An item that's dropped will have an ilvl equal to the mlvl. Items that are bought have ilvl equal to clvl (character level) + 5. There's a cap on the ilvl of items bought in normal, but not in nightmare or hell. Items that are gambled have ilvl equal to clvl - 5 to clvl + 4 (randomly).
However, for calculating what affixes are possible on an item, you also have to take into account the qlvl. This number is the same for all items of a given type. For example, all boots (regardless of what stats they have and who found them where) have qlvl 3, all demonhide boots have qlvl 36 and all wyrmhide boots have qlvl 60.
If you gamble at clvl 81, the worst case ilvl would be 76. If you craft with the same character, the crafted item's ilvl will be 78.
However, it turns out that all three kinds of boots will still have an alvl high enough to allow the greatest resistance affix on boots: up to 40% to a single resist. So you were just unlucky.
However, for calculating what affixes are possible on an item, you also have to take into account the qlvl. This number is the same for all items of a given type. For example, all boots (regardless of what stats they have and who found them where) have qlvl 3, all demonhide boots have qlvl 36 and all wyrmhide boots have qlvl 60.
If you gamble at clvl 81, the worst case ilvl would be 76. If you craft with the same character, the crafted item's ilvl will be 78.
However, it turns out that all three kinds of boots will still have an alvl high enough to allow the greatest resistance affix on boots: up to 40% to a single resist. So you were just unlucky.