Why not slipstream ZDP fixes into the bits downloaded by the installer rather than being a separate download?

In a comment on my discussion of ZDP fixes, cheong00 wonders why the ZDP isn’t just slipstreamed into the bits downloaded by the installer. That way, when you install, you get the latest version right away and not have to wait for a separate patching step.

There are multiple steps of installing, and they may take place at different times.

1. When you download the installer itself.
2. When you run the installer to obtain bits.
3. When you install those bits.
4. When you boot up with those bits.

The interesting period for the purpose of this discussion is the time between the steps 2 and 4. If that time period is very short, then the bits obtained by the installer contain all the latest fixes, and the search for a ZDP in step 4 comes back with “You’re up to date. No worries.”

The problem comes when the time period between steps 2 and 4 is very long.

For example, you buy a packaged product from the store. (Yes, you can still get packaged product for Windows. Dunno if they are still available in stores. Or if stores even still exist.) Who knows how long that box has been sitting on the shelf, or in a warehouse before that?

An even more extreme case of this is the computer with Windows preinstalled. Computer manufacturers typically require several months of lead time before a computer finally hits store shelves. They need that time not just to run their own acceptance testing on the latest version of Windows. That time also is incorporated into each computer that is manufactured: After the operating system is installed and the computer passes quality assurance, it is packed onto a cargo ship for a long, slow trip across the ocean. And then it arrives in a warehouse and gets moved to another warehouse, and then it sits in that other warehouse for several weeks before it goes out to a store, and then it sits in the store for several weeks before somebody buys it. (This entire process is known in the jargon as the channel.)

This means that the copy of Windows on the computer you just bought is typically several months out of date even before you even turn it on.

That is the scenario that the ZDP is designed for, and which I sort of put forth as the scenario in question in the original article: You unpack a computer from its box, turn it on, and OOBE¹ runs and checks if there are any updates that came out since the bits were originally obtained.

So going back to the original question: Yes indeed, the installer downloads the latest bits, including any ZDP fixes. But the problem is that at the time the installer downloads those bits, there may not be a ZDP yet.

¹ That Wikipedia article is confusing. It includes the sentence “The OOBE can also include the complete lack of such wizards.” I don’t know what it means when you say that a program include the complete lack of something.