The knock spell appears to have been modified so that it now only affects locks with a DC of 25 + the caster's level. The standard wand of Knock only has a caster level of 3, so anything above DC 29 will not be affected. There is at least one other item in the game that uses knock, but its caster level is 11. Obviously, this is a superior item than the standard wand.
Something else of related interest, the crafting system allows you to set the caster level for items that you can create. Thus, if someone creates a Wand of Knock, this can be much more potent than the standard model.