There is a big difference between an OEM_SLP Key (from the likes of Dell) and an OEM_NSLP (System Builder) Key.
The System Builder Key should activate over the internet from the get-go.
Many people don't have a clue which Key is in use on their machine until they come to a reformat/reainstall. or the OEM_SLP self-activation breaks down. Once the COA_SLPKey has been activated once on that machine, it will quite happily re-activate again over the internet, even if the machine has been reinstalled with the proper OEM_SLP and Recovery disks in the meantime.
I'm quite prepared to believe that these things can happen - but since my MS source tells me the normal procedure is for telephone activation, that is the expected route, as far as I'm concerned.
We've been down this discussion before - and there is no point in continuing it wither way. At the end of the day, what matters is that one way or another an OP's computer gets activated with a genuine key and valid license.