Hi Zen,
I don't have any special knowledge,but here is my option on the version #'s of agents :
The agents are still being advanced and fixed, as fast as they every were. I think the version numbering of agents is more aimed at an easy transition during the last two years, and backward comparability.
The policy server releases underwent a bit of a transition to their 64bit releases in the R12.6+ releases - but the agents already had 64bit releases. Agents released at the R12.52 SP1 level are comparable with policy servers from : R12.52 Sp1 policy servers all the way to R12.8 policy server. So by keeping the agent releases at the R12.52 Sp1 stage, there is only one stream of updated webagents to keep track of not several.
I expect sometime in the future the agent release stream will converge again. CA SSO Access Gateway is also evolving with it's move to 64bit (in R12.6+) and as it incorporates OpenIDC and other functions - but no I do not think it's a plan to replace all the webagents with Access Gateway.
Cheers - Mark