1) The use of Rupture will not have an overwhelming impact on your DPS either way. If a person was playing a rogue badly with Rupture, they'll still be playing it badly without it.
2) This guide is -- heck, virtually any guide is -- intended to provide a sense of what a person *should* be doing, not what other people *are* doing. If Rupture is mathematically a DPS gain, then it's mathematically a DPS gain regardless of whether top-performing rogues in top-progression guilds raiding during the first week of MSV have elected to use it.
3) There can be any number of reasons why, in the first week of a raid tier, people choose not to use a particular ability or rotation (or spec, for that matter). Theorycrafting isn't necessarily complete or conclusive on a wide range of issues yet, and inertia is a powerful force.
4) The
top Combat parse for Feng at the moment was posted by a Rupture-weaving rogue. So your use of "all" is probably an overstatement.
I haven't seen any evidence in this thread or others to suggest that the Rupture recommendation is wrong. I suppose it could be; maybe the data analysis that led to the statement being made in the OP is no longer current. And as Pathal noted, the guide itself needs a person to love and hug and squeeze it and keep it up to date and accurate.
But "rogues in some logs I looked at didn't use it" doesn't automatically flow into "clearly the guide is wrong." There are confirmatory steps that have to happen between those two points. The tail doesn't wag the dog.