I think Wikipedia is in the wrong here. In fact, if you read the article linked from the disambiguation page, it strongly supports the definition shown in all dictionaries, and makes no mention of rocks or chairs being 'amoral'. Regardless, none of this bears out the idea of 'amoral' meaning morally agnostic, ie actions having no moral component, and your initial semantic nitpick was itself incorrect.
Dictionary.com: having no moral standards, restraints, or principles; unaware of or indifferent to questions of right or wrong: a completely amoral person.
Merriam-Webster: lacking moral sensibility <infants are amoral> | being outside or beyond the moral order or a particular code of morals <amoral customs>
Apple dictionary: lacking a moral sense; unconcerned with the rightness or wrongness of something : an amoral attitude to sex.
thefreedictionary.com: Lacking moral sensibility; not caring about right and wrong.
Admittedly, some of these do mention definitions along the lines of "having no moral component", so it looks like everyone was wrong. Hurray!
