Even if people are paying based on CPM they're going to be expecting some sort of return on their investment from the traffic source. So if they're running ads that have dates, that are now basically worthless, they're PROBABLY going to get a lower CTR, resulting in a lower conversion rate, and are probably going to look like idiots in the process, or their brand will anyways.
If they get a shitty ROI from their investment on ads on Digg this time why would they be inclined to use Digg in the future? You probably wouldn't keep running your ads thru Miva or on Yahoo's content network if you got a shitty return, would you? Your probably going to want to utilize the traffic sources that are constantly giving you a good return.
It just makes Digg look bad in my opinion. (When it's probably FM or DoubleClicks screw up for running the wrong creatives)
Hope that explains my logic and redeems myself NickyCakes