We don’t know why Microsoft chose the offset size of 63 sectors
Come on....really? Don't you know your history? I'm really dissapointed.
CHS, Extended CHS does not ring a bell?
XP chooses 63rd sector because it receives 63-sector geometry from BIOS. This was made a standard for LBA to CHS translation in the '90-es. And since early DOS-es, the MBR was the 1st HDD sector and the 1st partition started on the 1st sector ON THE 2ND CYLINDER. So if you manage the BIOS to report 32-sector geometry, XP will create the partition on the 32nd sector. But this needs to be made by ALL BIOSes, otherwise you return to the post-CHS pre-LBA compatibility (that is moving the HDD between 2 computers). So instead of waiting for BIOSes to be fixed, they choose the workaround, which only works on the 1st partition.
And if you format a partition disregarding CHS (let's say with Vista) and then install XP on it, I see no problems. So XP's problem is actually XP INSTALLER's problem.