It's an open secret in the tech industry that if you buy a conference sponsorship your company gets a speaking slot in return. These speeches are not labeled as ads. Of course that ruins any transparency they might hope to have.
I found out about this when I ran the first BloggerCon at Harvard in 2003. I asked for sponsorships from some of the biggest names in the tech industry, and was told by each of them that they required a prime speaking spot as quid pro quo. I said maybe they could sponsor a meal, and speak at it, but I'd have to label them as paid speaking slots. I was told that was not acceptable. I told them to keep their money. We'd find a way to make it work without sponsors, and we did.
I was an adviser for another conference that I won't name. I went to several all-expense-paid meetings. Until it came up that their sponsors got speaking slots as a quid pro quo. Not disclosed to the participants. I didn't go to another meeting (and I didn't make a stink about it).
I'd love to hear from each of the tech pubs that run conferences that they don't do pay-to-speak. I suspect you won't hear most of them say it because they do it. That's how they make money from the conferences, which are really, mostly sales events for the sponsors.