There are many smaller brands and millions of generic no-name desktop computers call “white boxes” that get sold every year. All of these generic computers fly under the radar, and no one keeps track of what is going on. It is a perfect place to hide a million or so Hackintoshes from public scrutiny - and especially from Microsoft.
An extra million copies of Mac OS X 10.6 sold will look like more people are upgrading from Mac OS X 10.5. Analysts will just report how great Apple is doing getting people to switch. But Apple will have the actual sales data, and it will be able to spot any unusual trends.
A million Hackintoshes should not go unnoticed. They have probably estimated within a few percent exactly how many people will switch.
In order for Apple to see the spike in demand, everyone needs to wait a few months and then buy the full copy (not the upgrade). This will send a strong message to Apple when it sees the spike in full copy sales. (It’s even better if you buy the family pack and build five Hackintoshes.)
Apple is a software company, but it’s also a hardware company — their software just drives people to buy Macs. Doing this would cripple the company.