The dotcom era had incubators through models like "I have access to capital but no one good idea; let me start a bunch and pick which to go". VCs regularly host EIRs (entrepreneur-in-residence). More dominant, many universities, corporates, and in gov, SBIR. Not sure how the numbers of SBIR compare to YC, but given SBIR is based on a % of each US dept's budget... ;-)
The "startup accelerator" changed the model: more $ to more varied entrepreneurs, structured program with educational eco-system, made VC capital more attractive, etc.