When installing Windows 7 Professional on a Lenovo Thinkpad T430 (that has a real SLIC), during the OOBE it skips asking for a product key. No unattended file. Is the SLIC related to this?
Yes , much like when Win8.x/1x setup detects a valid MSDM table/key it will skip the OOBE screens for a key and edition, on Vista/7 kernels usually it will skip that key entry screen, it will still give you 30 days to activate. If the iso has a OEM Lenovo Certificate and SLP key for the edition you installed then it will offline activate. Or use Daz's loader to install the Cert/Key for Lenovo.
I used Daz Loader to activate (and it installed just appropriate certs and keys, no bootloader as real slic is present) I believe the reason why certs + keys don’t come with retail ISOs is so people won’t pirate different versions of 7/Vista (ultimate cert + key on a home premium system?) and piracy in general.