The Sims 2 has always used SecuROM since its release in 2004. This wasn't some "surprise." They just failed to remove it for the Origin version, and judging by the hacks and workarounds some people have had to use to get it to run on Windows 7/8 or at a 16:9 resolution, I'm sure they did absolutely no work to update or modify the Origin version. That's why it has SecuROM. Not as some backdoor to install it. It's not some secret. They're just not wasting time modifying something and then having to do new quality assurance on it to give away a free gift as a short term promotion to get people excited for The Sims 4 (which, by the way, will also have some form of DRM, I guarantee you).
And as I said in my original post, if you really are not willing to trade away a tiny amount of freedom for the right to play a video game, you're also highly unlikely to install Origin in the first place (which is an always-only DRM system), and won't have access to this deal to begin with.