I have a hunch that all free spins aren't as truly random as they appear to be. I know I mentioned this in another post but this thread is more appropriate. Avalon and Kathmandu have an extra wild symbol during the free spins — this sends off bells in my head indicating that something is clearly different during the free spins. These symbols seem to appear all the time during normal spins but not very often during free spins.
In Ho Ho Ho and Halloweenies, I tend to get excited when I see the spins being retriggered, but I notice that when they are retriggered, there tends to be that many more spins which yield nothing at all, essentially negating the retriggered spins. So I'm not sure everything is 100% as random as it is on a normal spin, but then again, who says it has to be? As long as it appears to be, that's what makes it fun.
RTG games also have a lot of differences during their free spins so I think that these features are probably more controlled than they appear to be, no matter which software you are using.