That's more or less the way IBM, HP, EDS, Infosys, Wipro, SAP, Keane, Red Hat, and Pivotal work. As I understand it, they all get paid some for selling software, but they get paid a lot more for performing professional services — a lot of which are pretty closely analogous to manning the support lines.
The old statistic was that about 95% of programmers were working on company-internal projects, which means they don't get paid royalties for their code, because there are none. Instead they get paid, at least in theory, for satisfying their company-internal clients — whether that involves writing good working code, writing nonworking code, or answering support calls.