"Timeslip" dit :
First, Fallout doesn't use a 'lite' version of securom. It's the full thing, complete with system driver, explorer extension, (both of which are always loaded, even when fallout isn't running,) registry entries, etc. If you have autoplay turned on, it's all installed the moment you insert the cd.
Second, you don't actually need to install any of it. Bethesda implemented it in such a way that none of the required files for installing or playing fallout are protected. There's no way that was done purely by incompetence, so it would seem that Bethsda deliberately set things up so that any of us who have a problem with securom aren't required to use it. The fact that it's on the disc at all while not providing any actual copy protection whatsoever and being trivial to avoid would suggest that Bethesda were forced to use it against their wishes, (or against the wishes of whoever was tasked with implementing it, anyway,) so I don't intend to keep giving them a hard time over it.
Edit: It may well be a sony thing. Securom first started appearing on oblivion discs about the time it was released on ps3 iirc. It certainly isn't on my original disk.