GabeN's personal financial stake in Valve likely realizes much more in the way of a) cashflow and b) control than any rocker's relationship with their catalogs.
Newell isn't the ageing rocker, smarting over the unfairness of the contract, he's the old-school cigar-chomping record executive, deigning to allow others to enrich him with their art. If he wants more money, he's just got to wait around for a bit. It'll arrive presently.
