Worse than that - people will start tagging "this value is a Date" via comments, and you'll need to parse ad-hoc tags in the comments to decode the data. People already do tagging in-band, but at least it's in-band and you don't have to write a custom parser.
See also: postscript. The document structure extensions being comments always bothered me. I mean surely, surely in a turing complete language there is somewhere to fit document structure information. Adobe: nah, we will jam it in the comments.
"Use of the document structuring conventions... allows PostScript language programs to communicate their document structure and printing requirements to document managers in a way that does not affect the PostScript language page description"
The idea being that those document managers did not themselves have to be PostScript interpreters in order to do useful things with PostScript documents given to them. Much simpler.
For example, a page imposition program, which extracts pages from a document and places them effectively on a much larger sheet, arranged in the way they need to be for printing 8- or 16- or 32-up on a commercial printing press, can operate strictly on the basis of the DSC comments.
To it, each page of PostScript is essentially an opaque blob that it does not need to interpret or understand in the least. It is just a chunk of text between %%BeginPage and %%EndPage comments.
This is tremendously useful. A smaller scale of two-up printing is explicitly mentioned as an example on p. 9 of the spec.
