The point is that all those cloud features are enabled by default and difficult to opt out of.

I for one will not upgrade to Windows 10 until other people have identified all of the crappy cloud-based features (Microsoft Account, OneDrive/SkyDrive, Cortana, etc.) and written blogs on how to disable them permanently. Then I will do a clean install, disable all the crap, and only then connect the external drive that contains all my files.

Most people, though, will not be so cautious. If something is enabled by default, 99.9% of users will just keep it enabled, even if it's possible to disable it. After all, that's the whole point of enabling something by default.

But I'm sure it'll do wonders for their cloud service user engagement metrics. look how many people are using Bing / OneDrive / whatever

That's exactly the problem. The insightful videos on Microsoft's Channel 9 made it clear that they went crazy with Metrics since Windows XP. What they don't get or simply ignore are the huge user base of power users and developers that deactivate the "phone home metrics systems" in Windows XP and newer. That's why they introduced the Ribbons-menubar and Metro-/Modern-UI - they believed or tried what they wanted by using skewed statistics based on one-sided metrics.

His point seems to be that he never opted into our was even informed of his my documents being synced to skydrive.