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.  

Conferences that do not do pay-to-speak: Mesh, PaidContent, BlogHer, 0redev, Gluecon, IIW.