Scans are used to help keep an eye on the degredation of a disc, when used over time, This can help norrow down what are considered good discs. Over time Verbatim and TY proved themselves to be manufacturers of good quality stuff.
A poor scan after a burn could indicate a number of things:
Poor media, write stratagy for a particular MID, bad combination of media/fw/drive, etc. They should not be relied on as the be all and end all of if a disc is good.
Some with more experience maybe able to extrapolate a likelyhood of how well a disc can perform overtime from their experience with certaintypes, though this is not a fact of truth.
In the example given people maybe waiting to see how well it looks after a scan to see if it has a good compatability with their drive and firmware. If so they may then buy them and then have the test of time to see if they were worth the effort.
There is only one true test of coasterdom or good burn and that is: Does the disc work?