AMD did not chance the CPUID in order to preserve compatibility between Sempron and the tremendous amount of both installed AMD systems and available motherboards. The efforts for creating Sempron were likely a matter of hours only.
As the Sempron birth is nothing else than a simple renaming of AthlonXP, the consequences for customers and motherboard makers are small. If you don't mind your motherboard displaying AthlonXP at boot time, you don't even require a BIOS update.
We used two DDR333 DIMMs from Infineon that AMD shipped with the reviewers' package. Running at CL2.5-3-3-7 they are nothing special, but that resembles the typical memory that is installed into value systems.
The Socket A Sempron can be considered an easy deal for upgrades, as it will immediately run on all motherboards capable of running at FSB333. It's similar with the Socket 754 Sempron, while hardly anybody will pick this one as an upgrade path.