I honestly don't even think I noticed that they weren't red until I heard other people complaining about it. I usually only used the center point with the 5DII so whether or not it was red was irrelevant. But with the 5DIII the autofocus is amazingly accurate, I don't need a red confirmation of how accurate it is. But I guess for some it's important, but it seems like some people are just using it as an excuse to bitch about the 5DIII.
I just recently added a 7D to go along with my 5D II, and didn't notice the lack of blinking red in AI Servo mode until I read about it in the manual. For what I shoot, it doesn't bother me.
That said, there are people who like the blinking red and are used to it. It also seems strange that it is not an option. I do think people are overreacting about selling the camera off or switching brands because of it, but I suppose that it one way to get Canon to pay attention.
Strange though that there was no out roar about it in the 7D, and professionals were certainly using it. I have seen more than a handful of Getty photographers at various sports games using the 7D.
Have you actually compared a 7D with a 5D MK III? I have! They are not the same. The 7D lights up nicely in one shot mode for about 2 seconds, you can see the selected AF point clearly.
The 5D MK III, on the other hand, has 61 tiny AF points that are difficult to see, and the light flickers for maybe 1/10 sec, you don't have time to make sure your subject is under the tiny point, and, in low light, thats the only chance you get.
Those who have not used both seem to have lots of expert opinions!