What does Scrum have to to with allocation of development resources
Scrum in-and-of-itself isn't really critical to the issue I was attempting to address; I was only using it to help illustrate that development teams do not have unlimited resources. Scrum is simply one of the tools that my particular team uses to organize and prioritize our workload, so that we can appropriately allocate what limited resources we do have. I hypothesized (within the context of the original thread) that Valve likely uses some similar management methodology to organize their own workload.
Also, not every dev shop has a dedicated "maintenance team"... I work in a small dev shop where all of us cross-task to both development and maintenance. So in my case, it's absolutely a given that higher priority tasks (such as new development of a highly anticipated game, for example) would take resources away from lower priority tasks (such as maintenance of a game that's over a decade old, and not bringing in any cash at all for the company).