Best I can tell (and I haven't done much experimenting), Spartan Ops chapters/episodes are actually streamed content. The maps and char/object models are already on disk, but the videos, cutscenes, and mission scripting are downloaded when a mission is initiated. If that is the case, then it's not actually be possible to play Ops without an internet connection, because the necessary mission data can't be accessed. In short: Spartan Ops is not entirely "on-disc." This sort of setup would save hard drive space, and partially explain why Ops maps are reused so much. Just a theory though.
Even if this is the case, it does seem a bit unfair that a Gold membership would be required to access the content. Spartan Ops is a lot of fun. I wouldn't call it a substitute for Firefight, but it is certainly distinguishable from the Campaign in a way that adds replay value. I agree with Josh X574; Halo 4's offline content can get kinda stale. I bet 343i could reach a larger audience by extending Ops at least to XBL Silver members. Maybe Ops could be made downloadable to a USB flash drive, which could then be transferred to the X360. Some folks may not have their console connected to the internet, but I imagine nearly everyone can access the internet from a computer nowadays. Or, each season could be sold on a disk. Or several seasons on one disk. I have no idea how much memory that would require. Definitely a neat idea though.