Apple did the same thing with the DTK hardware... they released a "Software Update" version, with a letter revision to the same build #'s, and it was to enforce security and/or entrap those running the 10.4 Intel build on non-Apple P4 hardware. Get it? Apple Software Update connects to Apple servers, so they know exactly to whom/what/where their "update" is being sent and installed.... then they cross-reference those IP's against logs of ADC member logins (and this is only necessary when assuming the user submitted false info during the Leopard registration, instead of their real name/address). IP match? Boom! Gotcha.
Maybe they just want to see how many of those IP's belong to Microsoft's net. 🙄