I don't think we have done any "pick and choose" "among vendors" or "formats."
I would certainly disagree with this "history." When I first approached PG several years ago about how I could support the Kindle using the MOBI file format I was told to go stuff it because PG have chosen to support this cool format called "Plucker." And then more recently PG supported "ePub" completely including table of contents -- where ePub commonly *does not* follow the standards of ODF correctly (following instead an incorrect defacto standard set up by Adobe Digital Editions) but PG did not implement table of contents correctly for Kindle even though the Kindle MOBI standard *does* correctly follow the ODF standards. So the incorrect Adobe implementation was supported but the correct Kindle implementation was not. And when I pointed this out again I was told to go stuff it. Most recently PG seems to be getting this stuff correct on Kindle, but only after a couple years delay.