Google sometimes attaches patent licenses for non-aggressors for code they've open-sourced (see: WebM). That ties the hands of a future management: the relevant patents are only useful defensively. Anyone not suing Google (or a downstream user of Google's code) for patent infringement related to that code can take advantage of the freely available patent license.

Of course, they're not doing that for everything (e.g. PageRank patents), but to the extent that they do this for the patents they intend to use defensively, they might avoid this problem.