Because NAC integration is a crapshoot, adoption is slower than it otherwise would be. If that's to change, the three primary NAC standards creators--Cisco Systems, Microsoft, and the Trusted Computing Group--need to step up and create certification programs with logos that offer the assurance of interoperability. Certainly, Cisco and Microsoft have plenty of experience creating such programs, each having done so for other partner ventures. They also have a significant incentive--neither company makes every piece required to complete the NAC puzzle, so assembling a broad, trusted set of vendor partners is obviously good for selling the overall vision.
As for the Trusted Computing Group's Trusted Network Connect initiative, until recently I wouldn't have put much credence in a TNC logo program. There just hasn't been market interest, and a recent reader poll found that TNC had by far the lowest recognition of the three major NAC standards. I say "until recently" because Microsoft gave TNC a shot in the arm when it announced at Interop that it would submit its Statement of Health protocol for inclusion in TNC. The Microsoft protocol is used to send host health information to policy servers.
server operating systems TNC-compliant without having to do a lick of extra development. In addition, anyone with a Web browser can download the TNC specifications and integrate with Windows. This is a boon to NAC vendors, which have never wanted to develop, maintain, or manage their own Windows client software.