I see SSL's integrity channel as something which should simply always be there on any TCP frame henceforth. RSA key is simple to manage, and key management costs are marginal. The wonder of RSA math means only one side needs keying and substantial improvement in default end-end channel integrity is provided, always. They can use the default scalable authentication service provided by SSL which is application and stack and netweork and vendor and platform indepedent, else use their own proprietary design, as per NT's proprietary challenge-response mechanism on the web. Exploiting SSL basic integrity channel is simply a matter of organizing winsock hooks, not fighting over standards to win market share wars or level playing fields in infrastructure deployment battles.
Monolithic systems fail, as do monolithic standards.
If there exists an archictectural manner of providing the feature, then the standard offering has no reason to change, might be the rule. This very much looks like case of forcing a change to the deployed standard to simply ensure a different incompatible standard exists. The usual reason is marketing, and market share wars. Here are two recent messages to the IETF Transport Layer Security Working Group. That group is considering using SSL 3.0 as the basis for the TLS effort.