Everyone is likely to want to control the formatting of dates, so they put in support for that. I doubt it even occurred to anyone that someone was going to want to use a format specifier on a line length!
In hindsight, I'll admit my answer wasn't the best -- I was thinking about the case of userdata where the values are strings even if numeric. Might not be unreasonable to ask that you get the chance to apply a format specifier to something like the line length variable which is a number internally, but expecting OG to parse numeric userdata so you can turn around and round it off might be a feature request that takes a very long time to get to the top of the pile!
To get that feature request, or any other feature request, in front of the Omni developers, use Help->Send Feedback or email firstname.lastname@example.org
. That way it will be tracked and entered in the database. A forum posting right before Macworld and with everyone busily trying to figure out how to move all of the Omni products to the iPad stands a better than usual chance of being missed, I'll wager...