Personally I think there is a disadvantage to being the 'victim' of a walkover, or at least inconsistency. In the first instance if there is a walkover situation I think that there should not be a minutes penalty. If you look at the minutes allocated in the game in question there were nine people who dressed for the game. The starters got 36 minutes, back ups got 12 (4 each). The 9th person was the trainee and was booked to play the full 48. Instead he received 43 minutes. To me this doesn't make sense and the full 240 minutes (48 * 5 position) should be allocated. In this game I lost 5 minutes to the 'walkover void'. Had i dressed only 5 people I would have lost 25 minutes to the 'walkover void'? Point is there is a penalty where I'm not sure it is fair to have one, especially when you consider that you run the full risk of injury.
In short:
I think if there is a penalty on minutes, then at least make it so that injuries can't happen.
If however there is actually a 'game' with the lucky fans, then maybe allow injuries, but don't penalise teams in terms of minutes.
Not being able to always get 240 games minutes allocated to your players AND being 100% able to get injuries as if there is a game doesn't seem right.