If you purchase an O'Reilly book on Google Play Books, it includes both 'flowing pages' and 'original pages' format (the reading apps let you switch between them while preserving reading location)I believe you can download DRM-free ePub and PDF from there. For example:
https://play.google.com/store/books/...d=S_SJ2LaZH8EC
O'Reilly could offer 'Print Replica' editions on Amazon (as well as .mobi) but that storefront is not set up to offer multi-format purchases as Play Books is.
Safari Books Online is not likely to be the conduit for PDF downloads. O'Reilly is but one of many publishers there and many of the others continue to have their own storefronts (at least until now).