Over the years, many people have acknowledged that one of the "weaknesses" of the iMac was the optical drive. Perhaps having a vertical enclosure rather than a horizontal one may have been a factor. Whatever, there has been some displeasure with the drive.
Apple have decided to dispense with the optical drive, in part, to allow the iMac to be thinner. Their decision follows in the wake of the MacBook Air for example.
There are numerous good quality CD/DVD recorder/players on market. I rather presumed that the new iMac would include the appropriate software; but chscag who has forgotten more than I have ever learned about these matters suggests otherwise.
Even with in-built software, I have always preferred Toast Titanium by Roxio which does a great deal more than burn CDs & DVDs, but you have to pay for this.
Ian