No, it's neither semantic nor analytic--which would imply i'm setting up a model for the sake of analysis. My argument for this logical: that capitalism produces a certain kind of dominant social relation. I'll explain why below.
> But there is certainly a conceptually useful distinction between things that are placed within M-C-M' and things that are placed outside it.
Marx used the MCM' model to abstract the movement of social value (for private accumulation) in the process of production. This is only one aspect of capitalism, and the social relations of capitalism extend far beyond the point of production. Capitalist society is geared to "produce" a certain kind of subject, the wage laborer; so that one's entire life becomes something like a process of production. Not only does "society" produce you, but you produce yourself, make yourself more valuable for capital--but in the end, despite the slightly larger pile of crumbs you may accrue, you are still producing a more effective, productive subject for private capitalist accumulation. But this is systemic. One cannot simply opt out. Social relations form the conditions of possibility for our being in this world. This reaches far beyond the philosophy of the encounter (man with man, man with institution, etc.).
Remember though, there is a countervailing logic--the side of the working class: social value for itself, where we find freedom not in independence (as in capitalism), but rather freedom in dependence via social appropriation of social value. It's safe to say that we aren't there yet... nor is it inevitable.
This is all still vague, but I hope it's helpful.
best.