So far as I know, Amazon is the only other retailer to make that transition, and they still have only accomplished it in 2 markets. They first reported in May 2011 that the main Kindle Store had exceeded book sales on Amazon.com, and then in August 2012 reported that the same had happened to the UK Kindle Store at Amazon.co.uk.
eBooks.de has been selling ebooks since before 2005, though back then it was going by it's old name of Libri.de. They report having the largest collection of Mobipocket ebooks of any German ebookstore in 2005, and then moved over to sell Epub in 2009. They currently offer 600,000 eBooks in ePub and PDF format that can be read on eBook.de's reading apps for Android or iOS as well as any ereader which supports Adobe DE DRM.