If you'll notice, he explicitly uses the phrase "unobservable components of the universe's wavefunction", and the context is clearly many worlds quantum mechanics. This means your thought experiment is not at all analogous to his statement.
Your implied invisible (observer outside the light cone) is qualitatively very different then his implied invisible (unobservable components of the wavefunction). Your thought experiment shifts the focus by subtly redefining the original statement.
I'm actually with wedrifid here. I think the key point where wedrifid and I disagree is that I don't believe agents benefit from considering any kind of acausal trade or interaction. And it turns out that if you restrict yourself to physically interacting agents, you don't have to worry about unobservables. In contrast, if you worry about acausal interactions, it can make sense to worry about them.
Today's post, Living in Many Worlds was originally published on 05 June 2008. A summary (taken from the LW wiki):
Discuss the post here (rather than in the comments to the original post).
This post is part of the Rerunning the Sequences series, where we'll be going through Eliezer Yudkowsky's old posts in order so that people who are interested can (re-)read and discuss them. The previous post was Why Quantum?, and you can use the sequence_reruns tag or rss feed to follow the rest of the series.
Sequence reruns are a community-driven effort. You can participate by re-reading the sequence post, discussing it here, posting the next day's sequence reruns post, or summarizing forthcoming articles on the wiki. Go here for more details, or to have meta discussions about the Rerunning the Sequences series.