Of the hundreds of tech conferences, only five, Mesh, PaidContent, BlogHer, 0redev and Gluecon responded to the question in the first Pay-to-speak piece, all saying that they didn't do it. That leaves us to wonder about the others.
For example, Jason Pontin of Technology Review writes, via email: "Our conferences aren't 'pay-to-speak,' but sponsors are now fairly immovable on this issue: today, they won't sponsor without a speaking slot."
He continues: "We get around it the same way TED does: we invite potential sponsors to sponsor a lunch. It has the benefit of transparency, and (we think) better serves our event's attendees: insofar as a sponsor speaker has any value to attendees, he or she probably has more value if they speak openly about their products and services, rather than presenting themselves as 'thought leaders.'"