We are in an evolutionary stage in the ebook industry. The Pew study and the survey fail to even attempt addressing this critical issue. Specifically, the advent and availability of ebooks has not reached market and social maturity, so we really cannot extrapolate any long term conclusions from these types of studies. Consumers are still reacting to and absorbing the impact of ebooks. As in every market evolution, consumers' instincts will be driven by prior experience, which is the primary reason library patron's are still buying ebooks after checking them out. They are conditioned to do so.
There is a second reason that is not fully addressed. That is, library ebook delivery platforms are so clunky and painful to use that many patrons may have made the same decision I have. I would rather buy the book than check it out through the library, because the technical ecosystem in libraries is miserable and backwards. There is no attempt to measure how this may be affecting patron behavior in either the Pew study or the ALA/Overdrive survey.
Which leads us back to the simple reality that the broader and long term effects of digitization has been commodification. We see this with the internet, and with music specifically. We will most likely see it with ebooks as well. The ebook market and ecosystem hasn't reached that stage yet. But if it does we can expect to see these surveys and studies become outdated rapidly, because the defining characteristic of a commodity is its fungibility- that is, consumers don't care where they get it from, as long as it is available when they need or want it.
I may be wrong. Consumers may keep their old behavior of wanting to "own" their ebooks. But the industry here is pushing them away from that by not letting us actually "own" the books we buy personally anyway. This may not make sense to you if you have not looked into the legality of ebook ownership, but very few ebooks are actually sold outright- to anyone. Instead they are leased or licensed to a user. As consumers start to realize this, they may react indifferently, or they may think of ebooks more like data on the net. As long as they can get to it, they don't care if they own it. If the second scenario becomes reality (and it has with music), patrons will stop buying ebooks, and these surveys will be irrelevant.
Update: Shatzkin has a similar opinion.