FUD news cycle.
Replacement of buttery/custardy tones with diacetyl-free variants was being worked by DIYers and
eliquid suppliers back in 2010/2011.
Multiple suppliers officially came out with diacetyl-free formulations. Kudos to them
Some suppliers dropped eliquids, because they weren't content with the substitutes they could find for a particular mix. Kudos to them
Some suppliers supposedly stuck their heads in the sand, kept on using some flavors with the not-so-good flavorings. I have no idea if that still holds true in 2015 -- I've been strictly DIY for years.
It is always fair for a vaper to ask an eliquid supplier if they use any flavors with diacetyl or diketones (the broader category of iffy chemicals). If a supplier says they don't know, and won't check, I personally wouldn't use them. If they said a given eliquid does have them, I'd shy away from it unless it is something I vape very sparingly (again, personal choice).