Why would a qinggong monk ever take acrobatic steps over feather step? They cost the same amount but one lasts for a round and the other for 10 minutes per level. The 10 minute one also ignores all difficult terrain and the 1 round one only ignores the first 15 feet.
My purposed fix to this would be reducing acrobatic steps to 0 ki points. Then at least it serves some purpose.
My guess is this:
Acrobatic Steps is a feat, so activating it is a free action.
Feather Step is a spell, so the Ki power is a spell-like ability, which means it requires a standard action to activate, provokes attack of opportunity and is subject to anything that suppresses or dispels magic.
Feather Steps is still better in many cases since you can activate it before combat (if you're aware that combat is going to occur) and anti-magic isn't that common in most areas (unless your campaign takes place in/near the First World or in the Mana Wastes (I haven't read too much about the Mana Wastes, so I don't know if there are actually any rules for regions without any magical energies).)