MattP,
I too wondered this very question. We also do a lot of forming of "structural" materials, angles, channels, rounds, etc... My reasoning for this feature was to have a formed and unformed profile, much like sheetmetal, without having to create a configuration of one of the two shapes.
I tried using flex command to get the desired result, but on some parts it took more time, than I felt it was worth, to get the coordinate system setup for the trim planes. Quite some time back I had a short disscusion with Mark Biasotti of SolidWorks, on the SW forum, he told me this command was in no way created with this type of use in mind. So, it would definately have it's shortcomings.
I did send in an enhancement request for such a feature. Maybe you could too, at least I know I'm not the only one wanting something like this. If you're interested, I did model up a formed angle, much like you first asked about. Copy and paste this link(don't click on it), and you should be able to download it.
As everyone mentioned, it's not going to give you square outside corners, but you don't get them in a real life situation anyway.
Have a good one,
Chris